Insect-catching Plants, particularly of Cape Cod by Dr. Henry K. Svenson

Most people have an acquaintance with the carnivorous plants, ordinarily called “insectivorous plants”, since the subject is included in all textbooks that deal with natural history. Few plants have been so attractive to sensational fiction writers, but the man-eating kinds exist purely in the imagination. Most of them are small terrestrial plants of boggy or sandy places, but some Asiatic pitcher plants (Nepenthaceae) climb or are bush-like. All have normal chlorophyll in stems and leaves; in addition there are adaptations for trapping insects, spiders, and other small creatures. Only in nutritionally poor environments is there need of additional protein, and the plants get along without it over long periods.

About 500 species of canivorous plants occur in six unrelated families over nearly all parts of the world, but they have greatest diversity in the tropics. As to methods of trapping insects, the plants found in eastern United States fall into three groups.

1. In the butterworts (Pinguicula, family Lentibulariaceae) the trap is slime secreted on the surface of the leaf. The leaf edge eventually rolls in over victim. There are about 40 species of Pinguicula. They are unknown on Cape Cod, but the blue-flowered P. vulgaris appears in northern New York and Vermont, and is a common plant in the moors of Scotland. Several handsome species accompany the pitcher plants of our southern coastal plain.

2. In the sundews (Drosera) and the well-known Venus fly-trap (Dionaea), both in the family Droseraceae, the insect stimulates a rapid movement of tentacles or other structures which hold the prey fast. Dionaea is restricted to the sandy coast of North and South Carolina.

3. In the bladderworts (Utricularia, family Lentibulariaceae), in the pitcher plants (Sarracenia, family Sarraceniaceae), and in the Asiatic pitcher plants (Nepenthes, family Nepenthaceae) the trap is constructed like a wire rat-trap or a lobster-trap. Slight movement has been noted in the bladders of Utricularia so that there is a faint transition here to the other trap methods.

PITCHER PLANTS. The common pitcher plant of eastern North America is Sarracenia purpurea, abundant in bogs from Labrador to Florida. It is now scarce on Cape Cod. I have seen it in Yarmouth and in Provincetown; and it is recorded also from Hyannis and from Monument Beach in Falmouth. The large purple flower, from a basal rosette of pitchers is too well-known and commonly illustrated to require description. Markings on the pitcher attract insects into it, and down-pointing hairs prevent them from getting out. At the bottom will be found wings and other hard parts left after digestion. On the coastal plain south of Richmond in Virginia, yellow-flowered pitcher plants appear in great patches in the damp pinelands. They are readily seen from train or automobile.

SUNDEWS. About 100 species of Drosera are known.. Most of them grow in damp places and commonly in sphagnum moss. In northern Europe are three species distinguished by shape of leaves. They are D. rotundifolia, D. longifolia (anglia), and D. intermedia. The round-leaved and intermediate-leaved forms are common on Cape Cod; the long-leaved is northern, and extends south only to Quebec. In the sundews, threadlike tentacles arise from the leaf surface. Each ends in a small slimy ball which gleams in the sunlight. These give rise to the poetic name “sundew”. The central tentacles are short-stalked; those at the margin are elongate. The marginal tentacles hold the insect down, and within a few hours these fingers of death have consumed the poor insect by means of digestive cells. After a satisfactory meal the tentacles become upright, and eventually the eyes, wings, and chitinous body are blown away by the Winds. On Cape Cod the thread-leaved purple-flowered sundew (D. filiformis) grows commonly at the sandy margins of ponds. The bulb-like bases, collected in winter, grow readily in damp sand in a window dish. It is known from Plymouth County, and along the coast to the New Jersey pine barrens, and in a somewhat larger phase along the Gulf of Mexico. The very numerous experiments with Drosera are described by Charles Darwin in a volume of 462 pages. As Wm. Irvine says in his readable and humorous book on Darwin and his associates, “Apes, Angels, and Victorians”, New York, 1955 (p. 204): “Darwin, having finished with man, fled happily to the other extreme of the organic world, resuming the study of his beloved Drosera, a rather messy little insect-catcher”. “The results of these delightful labors was ‘Insectivorous Plants’ (1875), a work full of the gusto of painstaking detail, measurements minutely exact, and ingeniously varied experiment.” Darwin even went to the extent of giving Drosera rotundifolia cobra poison. He worked on all sorts of insectivorous plants, including D. filiformis, and on the similar yellow-flowered Drosophyllum lusitanicum, which he obtained from sandy hills near Oporto.

BLADDERWORTS. Ten species are found on Cape Cod. An additional purple-flowered species (Uticularia intermedia) I have found just above the high-tide mark on the Agawam River at East Wareham in Plymouth County.

Since the Cape Cod sundews have been poorly collected, it would be interesting to prepare maps showing exactly where the various kinds occur on Cape Cod. I have found them most abundantly in shallow pond margins and backwaters in the Crooked Pond area of North Falmouth; also in the small ponds and pondholes east of the airport at Hyannis. Other places would probably turn out to be just as interesting. In preparing specimens the bladderworts are floated outon paper, just as with seaweeds. The following species of Utricularia are known from Cape Cod, based on the herbarium collections of the New England Botanical Club at Harvard University. Yellow-flowered: geminiscapa, vlugaris, inflata, gibba, cornuta, subulata, fibrosa. Purple-flowered: purpurea, resupinata.

The name “purple bladderwort” generally refers to U. purpurea, which is one of the commonest and handsomest species. The term “wort”, used only in compond words, is an old English word, pronounced “wurt”. Perhaps the rarest of these bladderworts on Cape Cod (I have not found it) is U. resupinata, known only from Crooked Pond, Falmouth; Griffith’s Pond, Brewster; and Simmons Pond, Dennis. U. biflora is known only from Crooked Pond, Falmouth; and Lake Wequaquet, Centerville.

The species of Utricularia are not always easy to identify. Reference should be made to drawings and discussions in Gleason’s “New Britton and Brown’s Flora”, and to Gray’s Manual; to the color photographs in Rickett’s “wild Flowers of the United States”, vols. 1 and 2; and to Seymour’s “The Flora of New England”.

The bladderworts have a complicated trapping system, devoted mostly to the larvae of Daphnia and Cyclops, which they entice by a sugary solution. They are widespread over the world except in the polar regions, and there are about 300 species, mostly tropical. Many tropical species are annual to perennial land plants with large flowers and complicated leafage. Some have subterranean tubers; some are epiphytic; some live in the tank leaves of bromeliads. On Cape Cod, U. cornuta, U. subulata, and U. resupinata are more or less terrestrial on muddy shores.

It is hoped that the reader will now investigate the great variation of the bladderworts, and will become interested in the species distribution of all insectivorous plants on Cape Cod.

DR. HENRY SVENSON’S botanical knowledge of the Cape Cod environment is unrivaled.

He has contributed a great deal of material and experience to the Museum’s Herbarium, and has donated some valuable books to our library.

He was a student at Harvard of Prof. Merritt W. Fernald, with whom he made a number of collecting expeditions on the Cape between 1917 and 1922. He received his Ph.D. from Harvard in 1928, and became Assistant Professor of Biology at Union College in Schenectady, N.Y.

Dr. Svenson was a curator at the Brooklyn Botanical Gardens from 1930 to 1946, and curator in the Department of Forestry and Botany at the American Museum of Natural History between 1946 and 1954. In 1941, he received a Guggenheim Fellowship, based on plant exploration in Ecuador and Peru. Between 1954 and 1966, prior to his retirement on Cape Cod, he worked for the U.S. Geological Survey in Washington as a botanist in plant geography.

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