2. Drosera Linnaeus, Sp. Pl. 1: 281. 1753; Gen. Pl. ed. 5, 136. 1754.
Sundew, catch-fly, dew-threads, droséra, rossolis [Greek droseros, dewy, alluding to glistening glandular trichomes on leaves] Sundew, catch-fly, dew-threads, droséra, rossolis [Greek droseros, dewy, alluding to glistening glandular trichomes on leaves]
Plants annual or perennial [rarely subshrubs], deciduous, stems 1–2 cm (except also caulescent stems to 8(–20) cm in D. intermedia), usually forming over-wintering buds (hibernaculae). on both surfaces in strong sunlight, greener in shade (except D. tracyi, which lacks red pigment even in full sun), unlobed, suborbiculate, orbiculate, spatulate, or obovate, or cuneate to linear pink, or rose to pinkish lavender; stamens 5, usually connate basally; gynoecium 3-carpellate; styles 3, deeply bifid; stigma capitate. Capsules obovoid, splitting between placentae. Seeds 20–70, <minute>. x = 10.
Species ca. 170 (8 in the flora): nearly worldwide.
Species of Drosera are concentrated in Latin America, South Africa, Madagascar, Australia, and New Zealand.
Droseras, like all carnivorous plants, have leaves that attract, catch, digest, and absorb nutrients from small, mostly arthropod prey. They are characterized by gland-tipped multicelled hairs that move in response to stimuli and that catch and appress prey to the leaf blade, where sessile glands secrete enzymes that dissolve the soft tissues. The released nutrients enhance growth by supplementing those available from the poor soils where they grow.
All species of Drosera are capable of moving their trichomes in response to contact with digestible prey. According to C. Darwin (1875), this movement can be induced by the mere touch of a part of a small insect with a single trichome. Besides having trichome movement, some species are able to curl their leaf blades to various degrees in order to maximize contact with prey.
Some species of Drosera may act as annuals, especially if the habitats dry out. The plants can be locally abundant. In most species, the flowers open only in the mornings on sunny days, or not at all on overcast days, and fruits may form from self-pollination. Some species, notably D. intermedia, may exhibit vegetative proliferation, portions of the flowers developing into leaves or plantlets. Some species form over-wintering buds called hibernaculae, requiring a cold period to break dormancy.
Some species of Drosera are reportedly utilized in herbal medicines to produce cough preparations and treat lung and skin ailments.
F. E. Wynne (1944) showed that seeds of North American Drosera are diagnostic for each species. The following key is adapted from various sources, and the species are presented in alphabetic order. Natural hybrids are rare in Drosera, and usually are sterile.
Hybrids: Many artificial hybrids have been made and given formal or informal cultivar names. The following sterile wild hybrids have been reported.
Drosera ×beleziana Camus (D. intermedia × D. rotundifolia): Nova Scotia, Michigan.
Drosera ×hybrida Macfarlane (D. filiformis × D. intermedia): New Jersey.
Drosera ×linglica Kusakabe ex Gauthier & Gervais (D. linearis × D. anglica): Quebec.
Drosera ×obovata Mertens & Koch (D. anglica × D. rotundifolia): British Columbia, southeastern Canada, Newfoundland, Quebec, Great Lakes region, northern California, Oregon, Washington, and New England.
Drosera ×woodii Gauthier & Gervais (D. linearis × D. rotundifolia): Quebec.
Drosera capillaris × D. intermedia, no hybrid name given: Pender County, North Carolina.
SELECTED REFERENCES Rivadavia, F. et al. 2003. Phylogeny of the sundews, Drosera (Droseraceae), based on chloroplast rbcL and nuclear 18S ribosomal DNA sequences. Amer. J. Bot. 90: 123–130. Shinners, L. H. 1962d. Drosera (Droseraceae) in the southeastern United States: An interim report. Sida 1: 53–59. Sorrie, B. A. 1998b. Distribution of Drosera filiformis and D. tracyi (Droseraceae): Phytogeographic implications. Rhodora 100: 239–260. Wynne, F. E. 1944. Drosera in eastern North America. Bull. Torrey Bot. Club 71: 166–174.