Flora of North America species comparison

Species ca. 170 (8 in the flora).

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. (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.

(Discussion copyrighted by Flora of North America; reprinted with permission.)

Drosera anglica is a boreal species that occurs on calcareous substrates. It often grows with D. rotundifolia in peat bogs, and with D. linearis and D. rotundifolia in marl fens, especially in the Great Lakes region. C. E. Wood Jr. (1955) presented a strong case for the hybrid origin of D. anglica, suggesting that it arose as a fertile amphiploid hybrid between D. rotundifolia and D. linearis. It is the only tetraploid North American species of Drosera with 2n = 40. The sterile hybrid D. rotundifolia × D. linearis may be found whenever these species grow together. To avoid confusion, and because a formal name for the sterile hybrid has not been published, it should not be called Drosera ×anglica Hudson, as is commonly done. According to D. E. Schnell (2002), the fertile species may be distinguished from the sterile hybrid by its wider flowers (8–10 mm versus 6–7 mm) and wider scapes (1.5–2 mm versus 1–1.2 mm).

The hybrid between Drosera rotundifolia and D. anglica is a sterile triploid, and has been formally named Drosera ×obovata Mertens & W. D. J. Koch.

Because Drosera longifolia Linnaeus cannot be convincingly typified and has been so often used for plants of D. anglica and D. intermedia in the literature (F. E. Wynne 1944), the name D. longifolia has been rejected as ambiguous.

Drosera anglica is found in the Aalakai Swamp at 1500–2000 meters on the Hawaiian island of Kauai (perhaps brought by migrating birds from Alaska); it is otherwise found in cold northern climates. D. E. Schnell (2002), who has grown the Kauai plants from seed, postulated that the high elevation provides a cooler temperature, and noted that plants from there do not form winter hibernaculae but only smaller winter rosettes.

(Discussion copyrighted by Flora of North America; reprinted with permission.)