Utricularia Bladderworts

These plants are dealt with together because three of the four genera are members of the family Lentibulariaceae (Genlisea, Polypompholyx, and Utricularia) and two of the four genera are primarily aquatic (Aldrovanda and Utricularia). They are lesser known carnivorous plants although they are just as fascinating to cultivate.

Utricularia _

HISTORY

There are almost 300 species of Utricularia distributed throughout the world from the tropics to the Arctic. Without a doubt, this is the most widespread genus of carnivorous plants.

The elucidation of the carnivorous habit of this genus began to unfold when Cohn, in 1857, discovered that they captured Perch fry. Both Cohn and Darwin thought that the prey pushed the trap-door open, entered, and when the door closed found themselves entrapped. It was Mary Treat, who in 1876, discovered that the prey did not swim into the trap, but rather were sucked in when the trap was set off and thereby captured.

Early observers, such as Cohn, Darwin, and Goebel, were aware that the prey disintegrated in the bladders. It was difficult to establish, however, if this was the result of decay or the action of digestive enzymes because of the small size of the bladders. Darwin's few experiments on enzymatic digestion produced negative results so he concluded that they did not. Luetzelburg in 1910 was the first to obtain evidence of digestive activity by enzymes in Utricularia. The extent of the role of bacterial action has not been established.

Both the United States Fish Commission and the Commissioner of Fisheries for the State of New York, U.S.A., published bulletins in the late 1800s on Utricularia under the title of Piscivorous (fish eating) Plants.

Utricularia is derived from the Latin word "utriculus" meaning little bag or s.n alluding to the traps of the plant. The common name Bladderwort originated from tlx bladder-shaped, traps of Utricularia.

NATURAL HABITAT

This is a very diverse genus of plants. Some aquatic species grow free, floating in water, while others float in water but are attached to the soil below. (Fig. 6-1) They grow in locations such as ponds and margins of lakes. The terrestial species grow in wet, acid soils while the epiphytic species grow on the surface of moss-covered tree trunk-, branches or stones. (Fig. 6-2) Some of the aquatic species tend to become terresti i.il while some terrestrials become aquatic and some epiphites tend to become terresti.il Some species are annuals while others are perennials. Those that grow in cold regions over winter by forming winter buds while some overcome hot, dry summers by forming tubers, often called corms, or by producing seed that germinates with tin-arrival of rain. While these plants are of world-wide distribution, none have been fou n. I on oceanic islands.

DESCRIPTION OF PLANT

Most of Utricularia spp. have long stems or stolons with varying degrees ol branching. Some species exceed lengths of 10 ft. (3 m). These thread-like, rootless plants have leaves that vary in size from insignificant to over 10 in. (25 cm) long. Then-is great variety in leaf sizes and shapes within the genus. There is a species, U. pubesccn which has mucilage on the upper surfaces of its leaves. It is not yet known whether prey captured by the mucilage is digested. Perhaps this plant has developed 2 methods of capturing and digesting prey.

The leaves of the terrestrial and epiphytic species grow upright. The distinction between stems, branches, and leaves is not clear. Modified stems called rhizoids anchoi some species in the growing medium. (Photo 6-1)

The distinguishing feature of this genus is their bladders or traps, which range from extremely small to lengths of up to xk in. (6 mm) and are all basically oval-shaped. The shape of the bladder is species specific.

It was once believed that the bladders functioned like pontoons to support the plan! and some even thought they extracted air from the water and stored it for the plant's use. But these beliefs were dispelled when it was established that the bladders trapped such prey as tiny animals, insects and baby fish (fry). The bladders grow on leaves of the aquatic species whereas bladders arise from any plant part of non-aquatic species. An unusual characteristic of these plants is that any vegetative part is capable of developing into any other vegetative part.

The racemose inflorescence bears personate flowers with elongated spurs and .i bilabiate corolla and calyx. (Photo 6-2) The throat of the corolla is usually blocked by <\ pubescent palate whose degree of exsertion is specific to the species. There are 2 curved stamens which may or may not be covered by the 2-lipped stigma. (Fig. 6-3) Flowei color varies by species and includes shades of yellow, white, purple, blue and red. In some epiphytic species the corolla diameter can exceed 2 in. (5 cm) and strongly resembles orchid flowers, while in most species the corolla diameter ranges from 0.08 1 in. (0.2-2.5 cm). (Photos 6-3, 6-4)

Both cleistogamous (a flower that does not open and is self pollinated) flowers and chasmogamous (flowers which are pollinated when open) flowers can occur on the same plant of some species. Evidence indicates that the environmental condition-, determine which kind of flower or if both will occur on a plant.

Annuals which survive the dry season by forming seeds are sensitive to water level fluctuations. It has been observed that if the water level remains above a critical level the plants will not flower at their usual time and contrariwise if the water level drops

Fig. 6-1 Aquatic Utricularia with flower.
Terrestrial Utricularia Traps

Fig. 6-2 Terrestrial Utricularia with scape.

with species. In some species the stigma does not cover the anthers and in other the anthers are partially or completely covered by the stigma.

below the critical level, a plant will flower regardless of how short a time plants have been growing.

Some species such as U. inflata produce tubers on the terminal ends of branches during periods of low moisture and/or temperatures. These tubers will germinate upon the arrival of suitable growing conditions.

TRAPPING

Closure of the Utricularia trap is faster than that of Dionaea. The door in the front of the bladder is attached to the top of the opening and swings open inward. The door is very elastic and when closed it rests on the edge of the door opening. There are projecting hair-like structures near the top of the door. (Fig. 6-4) These projections funnel the prey into the vicinity of the trap door.

The trap in all species is set by removing most of the water in the bladder. Water is removed by internal glands which excrete it. The removal of water inside the bladder results in lower pressure on the inside of the trap than on the outside. Consequently, the walls cave in giving the trap sides a concave shape. In this state, the door is forced tightly against the opening and no water enters the trap. If something touches or brushes against one or more of the trigger hairs on the door, the trap is set off. The door springs open, water gushes in carrying with it the prey. (Fig. 6-5) The force of the gush of water is often sufficient to jerk the whole plant. Apparently when the trap is set an extremely unstable equilibrium in pressure is set up, keeping the door closed. Therefore, only a very small force is required to set off the trap. Trapping usually occurs within 1/50 of a second. Traps usually reset themselves within 15-45 minutes.

Fig. 6-4 Utricularia trap. Hair-like projections funnel prey into the vicinity of the trap door.

While these plants normally capture very small animals, a trap can capture larger or longer creatures by sucking them in a little at a time-That is, after the trap is sprung part of the animal is sucked in, the elastic door closes around it, creating a water tight seal so that the trap can reset itself and again spring to suck in another part of the prey. Movement of the plant parts comprising the trap in the genera Dionaea and Aldrovanda is, in part, a growth phenomenon, whereas in Utricularia spp. it is the result of mechanical action.

Here, as in the case of some other carnivorous plants, digestion results from the action of enzymes secreted by the plant together with bacterial activity. There are organisms that live and thrive in the Utricularia spp. trap, feeding on the captured prey without themselves being digested. As wastes accumulate in the bladder, bladder color turns from greenish to dark purple to black and eventually the trap drops off.

Many instructive hours can be spent observing and studying the mechanism of trapping and the structure of the Utricularia trap. To observe trapping of prey and gross structure of the trap a magnification of 2-30 times is sufficient. Binocular or dissecting microscopes are particularly efficacious but a simple magnifying glass will reveal a great deal. Higher magnifications are required for examination of glands, details of the opening and other intricate parts of the trap.

Specimens to be examined are placed in a transparent container such as a petri dish or finger bowl. A pair of tweezers with fine points and a dissecting needle or two make manuevering the specimen into a favorable position for observation easier. Conventional dissecting needles are too large to open the door to the trap. They can be modified by grinding them into a smaller sharper point or by substituting a fine sewing needle in the handle.

DOOR

DOOR

Fig. 6-5 Utricularia trapping mechanism. The trap is set by removal of water from the bladder which results in lower pressure within the trap. A longitudinal section reveals the door is forced tightly against the opening. The trap is set-off when the trigger hairs on the door are touched. The door springs open and water rushes in, carrying with it prey in the vicinity. The door then closes entrapping the prey.

SPECIES OF THE GENUS UTRICULAR1A IN CULTIVATION

Of the almost 300 species of Utricularia fewer than one-third have been cultivated. To date this large group of very interesting plants has generally been ignored by carnivorous plant enthusiasts.

The Utricularia species for which cultural information is available are divided into 4 groups, with plants within each group having similar cultural requirements. They arc tropical, temperate, North American, and tuberous groups. It should be noted that the North American group includes all species that grow in North America, but does not mean that these species do not grow anywhere else, as many of them grow on other continents.

Group 1: Tropical Utricularia Species

Terrestrial U. amethystina U. calycifida U. dusenii U. inflexa U. jamesoniana U. leptoplectra U. lloydii U. livida U. praelonga U. prehensilis U. pubescens U. pusilla U. sandersoni U. scandens U. simulans U. spiralis U. subulata U. tricolor U. uliginosa

Summer temperatures: 65-95°F (18-35°C) Winter temperatures: 50-68°F (10-20°C)

Group 2: Temperate Utricularia Species

Terrestrial Aquatic

U. caerulea U. aurea

U. capensis U. hookeri

U. dichotoma U. lateriflora U. monanthos U. nova-zealandiae U. racemosa U. violacea

Summer temperatures: 65-82°F (18-28°C) Winter temperatures: 45-68°F (7-20°C)

Group 3: North American Utricularia Species

Terrestrial Aquatic

U. amethystina 2, also known as U. standleyae

U. cornuta 1 U. biflora 2

Aquatic

U. foliosa U. hydrocarpa U. obtusa U. stellaris

Epiphytic U. alpina U. endresii U. humboldtii U. jamesoniana U. longifolia U. nelumbifolia U. praetermissa U. reniformis U. unifolia

T"

Group 3: North American Utricularia Species (cont.) Terrestrial Aquatic

U. resupinata 1,W U. floridana 2

U. simulans 2, also known as U. foliosa 2

U. fimbriata U. geminiscapa 1,W

U. inflata 1,W U. intermedia 1,W U. macrorhiza 1,W, also known as

U. vulgaris and U. australis U. minor 1,W U. ochroleuca 1,W U. olivacea 2 U. purpurea 1,W U. radiata 1,W

Will survive freezing temperatures, but grow well and form winter buds with winter temperatures of 34-45°F (1-7°C). Summer temperature range 55-85°F (13-29°C) Summer temperature range 60-90°F (16-32°C). Winter temperature range 40-55°F (4-13°C). Form winter buds.

Group 4: Tuberous Utricularia Species

U. menziesii

This species grows in southwestern Australia during the cool winters and goes dormant during the dry, hot summers with just a viable tuber remaining in the soil. Summer temperatures: 70-100°F (21-38°C). Winter temperatures: 40-79°F (4-26°C).

DESCRIPTION OF COMMERCIALLY AVAILABLE SPECIES Terrestrial Species

Many terrestrial species of Utricularia have small, narrow leaves that are similar to minute blades of grass. It is much easier to identify these species by flower color and scape characteristics than by leaf characteristics. Some of the species often grow in shallow water, but they are firmly anchored to the soil.

U. amethystina (Also known as U. standleyae) The scape arises from a whorl of small blade like leaves. There are 2 smaller bracts between the large bract and scape. Flower color is variable, shades of white, yellow and purple.

U. capensis Leaves linear to spathulate up to 0.6 in. (1.5 cm) in length. One to 6 flowers that are all yellow or white or light blue with a yellow splotch on the palate.

U. cornuta There are 1-6 yellow flowers on a yellowish green scape that can reach a length of 13 in. (33 cm). The flowers have an unusually long vertical spur.Bracts alternate on the scape and a pair of smaller bracts occur inside the large one.

U. dichotoma Leaves narrow to oval-shaped up to 1 in. (2.5 cm) long. Bracts are spurred, opposite or in sets of 3. There may be from one to several light blue to purple flowers that may occur singly or in pairs of 1 or 2 or in whorls of 3.

U. lateriflora Spathulate leaves up to 0.2 in. (5 mm) long at base of scape. Two to 8 violet to purple flowers with a yellowish to whitish palate on each scape.

U. juncea Plant is very similar to U. cornuta except the scape is often purplish green and shorter, reaching lengths of 9 in. (23 cm). The yellow flowers number from 2-12, are smaller than those of U. cornuta, and can be chasmogamous or cleistogamous.

U. nova-zealandiae Leaves fan-shaped up to 0.6 in. (1.5 cm) long. Flowers purple to violet with vertical yellow lines on the palate.

U. menziesii During dormancy, the dry season, the above-ground parts of the plant

die back to an underground corm-like tuber whose shape and size is that of a rice graii 1 The single flowers are red with an unusually long, yellow, ridged palate. Bracts art-opposite or in sets of 3. (Photo 6-6)

U. -prehensilis Leaves are linear to narrow oval in outline and up to 5 in. (13 cm) long. One to 8 yellow flowers are borne on a scape that usually twines.

U. praelonga Leaves have a variety of shapes from short and wide to long ami narrow or ribbon-shaped reaching lengths of 8 in. (20 cm).

U. pubescens Leaves are round, peltate, horizontal and the upper surface is covered with mucilage producing glands. Diameter of the leaf blade is up to 0.2 in. (5 mm) with a vertical petiole that can reach a length of 0.4 in. (1 cm). From 1-10 white to light blur flowers are borne on each scape.

U. racemosa Leaves are circular to kidney-shaped. Numerous whitish blue flower*, are borne on a scape that often branches.

U. resupinata A single, purple flower is borne on a scape. Bracts occur in pairs opposite each other and are fused forming a tube that encircles the scape.

U. sandersoni The fan-shaped leaves are up to 0.8 in. (2 cm) long. One to 6 whitish to light blue flowers with violet streaks are produced in abundance the year around.

U. simulans (Also known as U. fimbriata) One to 8 yellow or yellowish white flowers are borne on each scape. The sepal and bract margins are feathered (fimbriate).

U. spiralis There are several varieties in this species. Leaves tend to be linear to somewhat oval in shape and are up to 2.4 in. (6 cm) long. Flowers 1-15, usually violet with a bluish green, yellow, or white spot on the throat. Scape usually twines.

U. subulata Two to 8 yellow to purple flowers with yellow-orange palates are born e on a zigzag scape. The bracts alternate on the scape. May have cleistogamous and/ot chasmogamous flowers.

U. violacea Leaves at base of scape are linear with filaments bearing traps. Bracts a re oblong, spurred and opposite on the scape. Flowers are violet.

Aquatic Species

U. biflora Stems thread-like, usually forming mats. Hair-like leaves bear traps. The base of the bracts clasp the scape which bears 1-2 yellow flowers.

U. floridana Thread-like leaves. Two to 8 yellow flowers are borne on a zigzag scape.

U. geminiscapa May have both chasmogamous and cleistogamous flowers. Plant is similar to U. macrorhiza, but smaller. Forms a winter bud. Leaves are hair-like. Flowers yellow.

U. gibba The hair-like leaves are alternate on the thread-like stems that often form tangled mats. One to 3 yellow flowers are borne on a scape that originates at the point from which several branches or stems radiate. Sometimes the branches creep along tin-bottom of shallow bodies of water. The rounded bracts partially clasp the scape. Ma\ form a winter bud.

U. inflata Has 4^17 yellow flowers on a reddish scape that is kept afloat by a whoi 1 of 4-11 inflated structures attached to the middle of the scape. Each structure or float is widest at its mid-point and tapers to its point of attachment to the scape. (Photo 6-5) The float also tapers from its midpoint to the free end which is finely dissected and bear, traps. Floats may reach lengths of 5.5 in. (14 cm). Bracts are oblong, pointed and longet than wide. Produces tubers when the environment dries out and during the winter Winter buds may be formed.

U. intermedia An aquatic which at times is anchored to the soil below the watei surface. Traps and leaves are borne on separate shoots. Has up to 6 yellow flowers. The middle of the bract is attached to the scape resulting in the formation of a lobe at the bottom. Forms a winter bud.

U. macrorhiza (Also known as U. vulgaris, U. austrais and U. macrorhiza ssp. vulgaris) One of the larger bladderworts often exceeding 13 ft. (4 m) in length with the stem ocea sionally branching. Leaf margins have tiny bristles. Bracts occur singly on the scape. It has 6-25 yellow flowers which have brown or red streaks on the palate. Forms a winter bud.

U. minor Thread-like stems usually form a jumbled mass. Has the same type of bracts as those of U. intermedia except they tend to be purplish. Tips of the leaves are serrated. Bears 2-9 yellow flowers. Forms a winter bud.

U. purpurea Has 2-8 pinkish purple or white flowers that have 2 pouch-like lobes on their lower lip. Bracts are attached above their base to the scape. Whorls of branching stems which bear the traps grow from the central stem, giving the appearance of many wheels with spokes on a single axis.

U. olivacea An extremely small plant. A single, white flower is found on each scape that is usually less than 1 in. (2.5 cm) high. A pair of leaves are located at the base of the scape with bracts alternating on it.

Epiphytic Species

U. alpina Leaves long, narrow, and terminate in an attenuate tip. Up to 6 white flowers with yellow palates. White, oval-shaped, subterranean tubers are formed that can reach 2 in. (5 cm) in length and which turn green when exposed to light.

U. endresii Leaves are up to 8.5 in. (22 cm) long and are similar to the leaves of U. alpina except they are narrower. Flowers are pale blue with yellow palates and number up to 6. The oval-shaped subterranean tubers are up to 0.5 in. (1.3 cm) long.

U. longifolia Leaves similar to those of U. alpina. Produces no tubers and has up to 10 mauve flowers with yellow palates or violet flowers with an orange palate.

U. reniformis Kidney-shaped leaf blade has a diameter of about 3 in. (7.5 cm) on a slender petiole that can reach 6.5 in. (17 cm) in length. Flowers are light violet with two, vertical yellow stripes on the palate. The tubers are almost spherical.

CULTURAL INFORMATION

Planting Media

Should be acid with a pH between 4 and 6.5.

Terrestrial species: Sphagnum moss living or dried, long fiber Or milled, sphagnum peat moss, various mixtures of peat moss with sand or vermiculite or perlite. Living sphagnum moss should not be used with the smaller species as it will quickly overgrow the plants.

Aquatic species: Grow them in any container such as gallon jars, mayonnaise bottles, aquariums, terrariums, plastic washtubs, or outdoors in pools, natural or artificial. If grown in containers, 2-3 in. (5-7.6 cm) of soil should be placed on the bottom.

Any planting medium may be used. If it is not acidic, the water can be acidified as per directions in Chapter 7.

If sphagnum peat moss is used, soak it for about 1 week, then remove any material that has not settled to the bottom with a strainer.

To condition the water for the plants, add a handful of sphagnum moss, living or dried, to the water if the medium is not sphagnum peat moss.

Water depth should be at least 6 in. (15 cm). Many aquatic and terrestrial spp. will grow in very wet watery soils, often referred to as slurries. A slurry is made by mixing 1 part sphagnum moss living or dried or sphagnum peat moss to 1 part water.The slurry is then put in a drainless container and planted.

Epiphytic species: Any of the planting media listed for the terrestrial species are used for epiphytes when they are grown in pots. Epiphytic Uticularia spp. can be grown in the same manner as the terrestrial species. If grown in hanging baskets or on boards, such as used for Staghorn Ferns, living or dried long fiber sphagnum moss is best Temperatures

As indicated in the table delineating each group of plants. Dormancy

The plants in Group 3 which form winter buds, called turions, are identified by the letter W after their name. The winter bud is usually a spherically-shaped body which may reach a diameter of V2 in. (1.3 cm) in some species. (Fig. 6-6) These turions tend to sink to the bottom of the water during the winter where they remain until spring

U. menziesii which is native to southwest Australia, grows during the cool moist winter and survives the hot dry summer as a dormant tuber.

Some of the species in Groups 1, 2, and 3 may stop growing during the winter but remain an evergreen.

Water & Humidity

Terrestrial species: These species are maintained very wet or waterlogged during the summer and drier during the winter. Uticularia menzesii—keep medium wet durinj; the growing season (winter) and dry during the dormant season (summer).

Aquatic species: Grow the species in acid water, pH 5-6.5. If the water becomes alkaline, algae growth can become troublesome. Kits used to measure water pH are available from stores handling tropical fish supplies. The same acids and procedures listed under Aldrovanda are suitable for use in acidifying water for Utricularia.

One grower has found that dissolving 1/10 of a gram of copper sulfate crystals in 18 fluid ounces (540 ml) of water and then adding 1 fluid ounce (30 ml) of this solution foi each gallon (4 liters) of water in the Utricularia growing container kills unwanted algae He warns, however, that the weighing and dilution of the copper sulfate crystals accurately is of the utmost importance to avoid poisoning the plants.

Epiphytic species: Thrive best when kept damp and in a highly humid environment.

Light

The North American species will thrive in strong light or full sunlight. The other species prefer indirect sunlight.

Artificial Light: Group 3 species 500-1500 foot candles during summer. Winter 100-300 foot candles for those not forming winter buds. For turion-forming species no light is needed during the winter.

Group 1, 2, and 4 species 500-900 foot candles during the growing season. Group 1 and 2, 300-700 foot candles during the dormant or winter season. Group 4 needs no light during the dormant (summer) season.

Photoperiod: Group 3 species Summer: 12-18 hours, winter: 8-10 hours for the evergreen species. Those forming winter buds need no light during the winter.

Group 1 and 2 species Summer: 14-16 hours, winter: 12 hours. These species can be grown year around with the same photoperiod. Our experience indicates that flowering is more regular when the photoperiod is varied and the plants are kept drier during the winter.

Group 4 species: 8-10 hours during the growing season (winter), none during the dormant (summer) season.

Pests

Aphids and fungus are the only reported pests. See Chapter 8 for control measures.

Feeding

Chapter 7 for directions.

Miscellaneous

Terrestrial and epiphytic species are the easiest to grow. While many of these species will flower in cultivation, none can match the profusion produced by U. sandersoni. Once established it flowers continuously year in and year out.

PROPAGATION

Sexual Reproduction

Some species have cleistogamous flowers, which do not open completely and will self-pollinate to produce viable seeds. The other type of flower which opens completely is called chasmogamous. Both kinds of flowers can occur on the same plants of some species. In some species the stigma bends over and covers the anthers, in others it is erect while in others the stigma bends over on itself, but does not cover the anthers. The anthers are positioned one to the right and one to the left of the stigma. (Fig. 6-3) The flower structure is designed to encourage pollen transfer by pollinating agents. To see the stigma and anthers, grasp the lower lip and the upper lip and gently pull them apart. The flower will open as if it were hinged and the floral parts are exposed so that one may pollinate them to produce seed or hybridize them. To our knowledge no one has attempted to hybridize this group of plants. As mentioned before, the flowers of these plants are designed to require a pollinating agent. Yet under some conditions some plants produce seed without an apparent pollinator. Perhaps movements of the flower induced by winds may dislodge pollen grains which tumble onto the stigma.

If the flowers are pollinated the ovaries will swell and in 4-8 weeks the seeds are mature which is evidenced by the almost translucent seed pod.

Seed from the species that form winter buds must be stratified to germinate. Seed not planted is stored in vials or bottles under refrigeration. Seed of terrestrial species is sown on the medium while seed of aquatic species is sown on the water surface. Seed germination is quite variable and may take up to 2 months.

Asexual Reproduction

Terrestrial species: Take a portion of soil with plants and divide it into 2 or more parts. Plant each part in a pot. They will multiply rapidly by vegetative reproduction.

Aquatic species: Cut the plant into pieces about 2-4 in. (5-10 cm) long and replace in water. Each section will develop into a separate plant.

Epiphytic species: Divide the mother plant into several smaller portions and repot.

Epiphytic species: Divide the mother plant into several smaller portions and repot.

Fig. 6-6 Some Uticularia species form resting structures called winter buds or turions. Turion tend to be spherically-shaped.

Fig. 6-7 Polypompholyx multifida plants including flowers, basal rosette of leaves and traps.

The two species comprising this genus grow in Australia. Both are very similar to the terrestrial species of the Utricularia genus differing only in sepal number and trap structure. Polypompholyx has a 4-part calyx whereas that of Utricularia is 2-part. (Fig. 6-7) Both species of Polypompholyx are annuals and are terrestrial plants.

Polypompholyx multifida, commonly known as Pink Petticoat, is found in West Australia. Narrow, oblong, green leaves seldom exceeding 2 in. (5 cm) form a rosette encircling the base of the scape. The scape can be up to 12 in. (30 cm) long and bears from one to several flowers on short pedicels. The flowers are various shades of pink with a yellow palate. There is a white flowered variant. The lower lip is 3-lobed and much larger than the upper. Flowers are usually less than V~k in. (3 cm) wide. (Photo 6-

Polypompholyx tenella, commonly known as Pink Fans, grows in West Australia, Victoria and South Australia. Flowers and leaves are similar to those of P. multifida except they are smaller. Scapes seldom exceed 3 in. (8 cm), leaves are not more than 0.5 in. (1.3 cm) and flower diameter is less than V3inch (0.8 cm). There are 1-2 pink flowers with yellow palates per scape.

Both species are annuals and will not self-pollinate. If they are grown in an area devoid of insects, the plants must be pollinated by hand to insure seed production. The flowers can be opened to reveal the sexual organs in the same manner as the genus Utricularia flowers. Pollen can then be transferred with a toothpick or brush from anther to stigma.

The trap in Utricularia spp. is attached to the stem at the end of the trap that is opposite from the trap entrance, whereas in Polypompholyx the entrance to the trap is on the same side of the trap as its attachment (called a footstalk) to the stem. The footstalk near the bladder is swollen, forming 2 ridges. The covering, called the beak or rostrum, is continuous with the top of the trap and divides to rest on each side of the footstalk. The rostrum touches the top of the ridge, blocking entrance to the lobby of the door from the front, but it forms two lateral wings anteriorly one over each side of the footstalk, resulting in funnel-shaped vestibules to the lobby. There are pointed hairs in

WING

WING

Fig. 6-8 Polypompholyx trap and longitudinal section through trap.

LOBBY

—VESTIBULE

Fig. 6-8 Polypompholyx trap and longitudinal section through trap.

the area of both vestibules and in the lobby that direct prey to the door of the trap.(Fij', 6-8) The overall structure of the trap is similar to a hand held palm-upwards with the fingers bent toward the wrist. The wrist is analagous to the footstalk of Polypompholy.x while the openings between the palm and index finger and pinkie are similar to the funnel-shaped vestibules leading to the lobby and the trap door. Like Utricularia spp the prey is sucked in when the trigger hairs are stimulated. Because of the close similarity of Polypompholyx to Utricularia, they are assumed to be carnivorous also.

Any of the planting media recommended for terrestrial Utricularia spp., except living sphagnum moss, can be used for these plants. Living sphagnum moss should not be used because it will quickly overgrow the plants. A temperature in the 70-100 T (21-38°C) range is suitable. Indirect sunlight is adequate. If artificial light is used start with 1000 foot candles and a photoperiod of 12-14 hours.

Aphids and fungus will attack these plants. See Chapter 8 for control of these pests.

Plants can be fed the same material as the terrestrial Utricularia spp.

Genlisea___

HISTORY

Auguste de Saint-Hilaire discovered the plants upon which the genus Genlisea is based in Brazil in 1833. Warming published the first thorough description of these plants in 1874.

NATIVE HABITAT

Genlisea species grow in tropical Africa, Madagascar, and South America in damp to wet soils. They are closely related to Utricularia, but the traps are distinctive. (Fig. 6-9)

DESCRIPTION OF PLANT

Rootless, herbaceous perennials or annuals having 2 kinds of leaves that arise from the slender rhizome. The linear or oblong foliage leaves which grow upward can exceed 2.5 in. (6 cm) in length. The second type of leaf, the trap leaves, are 1-6 in. (2.5-15 cm) in length. Scapes which can reach lengths of 16 in. (41 cm) bear several flowers which may be shades of blue, purple, violet, white or yellow. The flowers are very similar to those of Utricularia in structure, which have a 2-parted calyx whereas Genlisea has a 5-parted calyx.

TRAPPING

The trap consists of a footstalk which attaches the bulb or bladder to the rhizome From the bulb a hollow tube connects the bulb cavity with the cavities of 2 spiral or twisted cylindrical arms, terminating in an opening, the mouth. One of the arms twists clockwise and the other counterclockwise. This whole structure, called the trapping leaf, usually hangs downward in the water. (Fig. 6-10) The spiral arms can be likened to a long, narrow piece of paper folded in half along its longest axis and then twisted. The result is that the lower edge of the paper is shorter than the top edge. The space between the edges of the paper at each twist forms the trap entrances. In the arms the 2 layers of tissue are bound together periodically with special cells resulting in numerous separated entrances. Once the prey enters the trap, pointed hairs direct it toward the tube which leads to the bulb where digestion takes place or is completed and subsequent absorption occurs. Some botanists believe that the glands between the row of pointed hairs in the arms and tube secrete digestive enzymes and/or mucilage. In the

Fig. 6-9 Genlisia plant including inflorescence, rhizome with rosette of foliage leaves and trap leaves.

BULB

BULB

ENTRANCE

Fig. 6-10 Trapping leaf of Genlisia. The footstalk is attached to the rhizome and the bladder or bulb. The bulb is attached to the 2 spiral arms by means of a hollow tube lined with hairs. Insects enter the trap through the spaces in the spiral arms.

HISTORY

Aldrovanda vesiculosa was first observed in India in the 16th century. It was listed as Lenticula palustris Indica in L. Plukenet's, Almagestum Botanicum of 1696. The Italian physician, Dr. C. Amadei, sent some specimens collected from the Dulioli Swamp neai Bologna, Italy, to the botanist G. Monti. Monti subsequently named the plant Aldrovandia in honor of the naturalist, Ulisse Aldrovandi, in 1747. The name was altered, probably as a clerical error, to Aldrovanda which is now accepted as the correct name for the genus. Auge de Lassus in 1861, discovering that the traps closed, thought they were air storage organs to give the plant buoyancy in water. Darwin's expe riments with Aldrovanda indicated that absorption of prey took place in the traps and, realizing the similarity of this plant to Dionaea, assumed Aldrovanda secreted enzymes which digested the prey. Fermi and Buscaglione in 1899 confirmed that Aldrovanda did indeed digest its prey with enzymes produced by the plant. Common names for Aldrovanda are the Waterwheel Plant and Waterbug Trap.

NATURAL HABITAT

The aquatic plants grow just below the surface of fresh water in acid swamps, ditches and other quiet bodies of water in tropical and temperate regions. Its range includes Europe, Africa, Southeastern Asia to Japan and to Australia.

DESCRIPTION OF PLANT

Aldrovanda is a monotypic genus in the Droseraceae. The plant consists of a rootless stem whose length can exceed 8 in. (20 cm), and which tends to branch profusely, terminating in a spherical shoot tip with an abundance of protruding bristles. (Photo 6-8) Along the main stem and branches are numerous whorls of leaves arranged like the spokes on a wheel. Each whorl usually consists of 8 leaves about 0.5 in. (1.3 cm) long. Each leaf terminates in a trap which is usually flanked by 6 long bristles that extend beyond the trap. The plant grows by elongation of the stem and branches. (Fig. 6-11)

Flowers

In the spring small, white flowers are borne out of the water on short peduncles which arise from the leaf axils. The flowers consist of 5 petals which are longer than the 5 sepals, 5 stamens and 1 pistil with 5 styles radiating from the top of the ovary each of which terminates in a branching stigma. Up to 20, oval-shaped seeds are produced by the ovary.

TRAPPING

The traps are semi-circular in shape with about 40 trigger hairs on the inner surfaces, 20 on each lobe of the trap. Mucilage, digestive and absorptive glands are all located on the inner lobes. The 2 lobes are joined along the midrib in much the same manner as Dionaea (Venus Fly Trap) lobes. Trap closure is effected by stimulating the trigger hairs. Depending upon the age of the trap and cultural conditions, 1 or more stimulations are required, iiigh temperatures, chemicals and electricity will initiate trap closure. Surrounding the outer edge of the leaves is a row of very closely arranged epidermal hairs sometimes called spikes. These are organized differently than the marginal spikes of the Dionaea. In the latter the hairs lie in the same plane as the lobes and point away from the midrib area. In Aldrovanda the hairs point down into the trap. When the trap closes, the spikes intermesh as they do in Dionaea. This mechanism is

PETAL TRAP

BRISTLE

STIGMA

STAMENS

Waterwheel Plant

Fig. 6-11 Aldrovanda plant consisting of a rootless stem with whorls of leaves arranged like spokes on a wheel and flowers.

PETAL TRAP

BRISTLE

STIGMA

STAMENS

Fig. 6-11 Aldrovanda plant consisting of a rootless stem with whorls of leaves arranged like spokes on a wheel and flowers.

external with Dionaea, but is internal in the Aldrovanda trap. The intermeshed spikes serve as a sieve or strainer to keep the prey in the trap as it closes and water is forced out. An individual trap can close within 1/50 of a second and with such force as to visibly jerk the whole plant. As in Dionaea, the trap of Aldrovanda becomes narrower with adequate prey. (Fig. 6-12) It takes live, struggling prey to induce the trap to enter the narrowing phase. If digestible prey has been captured the trap will remain closed for about 1 week, if not, it will reopen in a few hours. Each trap can capture several meals before it is exhausted, but if too large a meal is captured, the trap will die. Since growth processes are involved in the working of the traps, increasing age leads to a decrease in functional ability.

SPECIES OF THE GENUS ALDROVANDA

Aldrovanda vesiculosa CULTURAL INFORMATION Planting Media

The plants require an acid water pH 6-6.9. Place at least 2 inches of garden, swamp or woodland soil or sphagnum peat moss in the bottom of the container which must be deep enough to provide the plant with a water depth of 6-12 in. (15-30 cm). II sphagnum peat moss is used, the moss will float for about a week until it becomes thoroughly wet and settles to the bottom of the container. (Strain the floating debris from the surface after the moss has sunk.)

After the water has cleared, check the acidity or pH with a pH meter or test paper. Kits for measuring pH are available from tropical fish stores. You do not need the whole kit, just the chemical bromthymol blue which is used as follows. Add 3 drops ol bromthymol blue to 2 tablespoons (30 ml) of water. If the color of the water changes to yellow it is too acid, if the water turns blue the water is sweet or alkaline and if it turns green, it is just right. If the water is too acid, add a very small quantity of a base such calcium oxide, calcium hydroxide, baking soda or sodium biphosphate. Wait a few hours and then check the pH again. Continue adding the base and checking the results until the desired pH is achieved. If pH is too high, that is, it is alkaline, add acid in the form of dilute sulfuric acid, citric acid, tannic acid, or acetic acid (vinegar) in small quantities until the correct pH is achieved. Some growers lower the pH by adding chopped straw, grasses, sedges, cattails, and pine or fir or spruce needles. A general rule is to add V4 cup (60 ml) of such plant material per gallon of water. In a few days the water will turn yellowish brown.

Another technique is to soak sphagnum peat moss in water for a few days. Drain off the water and add it to the Aldrovanda water.

Irises (Iris), rushes (Juncus), reeds (Phragmites), arrowhead (Sagittaria), and cattails (Ty-pha) grown in the same container condition the water for improved growth and flowering of Aldrovanda. Water color should be yellowish like beer or urine. If the water turns black, change it at once and review cultural conditions to prevent reoccurrence. The water should not all be replaced at one time in order to maintain a proper pH. Replace some each day or so with fresh water until the water has regained a yellowish color.

Temperatures

Aldrovanda plants grow in the tropic and temperate regions of the world. In some temperate regions the plants are subjected to freezing temperatures. Under our growing conditions the plants produce winter buds at temperatures below 50°F (10°C). We over-winter our plants at a temperature of 35°F (2°C). We maintain summer temperatures (growing season) in the 70-86°F (21-30°C) range.

Dormancy

In temperate regions Aldrovanda plants go into dormancy and form winter buds which settle to the bottom of the water until conditions are suitable for growth. In tropical areas the plants are evergreen and grow the year around. Therefore, they do not form winter buds.

Light

Aldrovanda is accustomed to and requires strong light for vigorous growth. The plants can utilize several hours of direct sunlight as long as the water temperature does not exceed about 86°F (30°C). Growth is poor above this temperature. If the plants are

MARGINAL SPIKE

TRIGGER HAIR

Fig. 6-12 Aldrovanda trap with inward pointing spokes which intermesh upon closure. Sequence of closure is from left to right. Final closure, the narrowing phase is induced by struggling prey.

tr growing in a container with transparent walls and placed in direct sunlight, the sides of the container should be covered with white opaque materials to prevent sunlight from overheating the water.

Direct sunlight tends to encourage algae growth, particularly if the water is not sufficiently acid. Algae growth inhibits Aldrovanda growth.

A grower reports that a product called Acurel E, available from Lilyponds Water Gardens, Lilyponds, MD 21717 U.S.A., will kill the algae without harming Aldrovanda. Four drops per gallon of water is sufficient. He advises that the water may turn purple but will soon clear.

Artificial light—1500 foot candles during growing season. Very little light is needed during dormancy. Photoperiod 14-16 hours during the growing period and 6-10 hours during dormancy.

Pests

None reported to date. Feeding

Adding fertilizer to the water for these plants is usually not advised as the fertilizer induces algae growth. Add very small water animals such as daphnia, water spiders, and microworms to feed the plants. See Chapter 7 for directions.

Miscellaneous

A few snails added to the water in a glass container will keep the glass walls clean. Some growers use aerators to bubble air through the water.

When the plants have elongated and branched out so that the surface of the water is occupied, further growth will be inhibited. In this case transfer the plant to a larger container or divide it and place parts of it in other containers.

If the cultural environment is excellent the terminal bud will be spherical and plump.

PROPAGATION

Sexual Reproduction

Aldrovanda plants require a pH of about 6, a temperature at about 77°F (25°C) and several hours of direct sunlight per day to flower and set seed.

We have hand pollinated the flowers and viable seed was produced. Their ability to self-pollinate in culture is unknown. Since it is rare for these plants to flower for us, we decided not to take any chances and hand-pollinated them. Based on our experience, light and dormancy seem to be the critical factors in promoting flowering once the correct environment has been established as indicated by vigorous growth and large plump terminal buds. The plants that have flowered for us are those grown in sufficient light and which have had a dormant period of near freezing temperatures.

Asexual Reproduction

Stem cuttings:

Cut the stems and/or branches in pieces 2-3 in. (5-8 cm) long in the spring and replace in the water. Each section will develop into a plant.

SECTION II

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