FNA: Drosera vs. Droseraceae

Distribution

Nearly worldwide

Discussion

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.)

Genera 4, species ca. 175 (2 genera, 9 species in the flora).

Droseraceae comprise carnivorous plants with an unusual, worldwide distribution. They live mostly in sunny, low-nutrient, moist-to-wet acidic sands, clays, seeps, and peat bogs, often subjected to periodic fires. They catch rather small prey in jawlike traps (Aldrovanda Linnaeus and Dionaea) or on sticky glandular hairs (Drosera and Drosophyllum Link). All genera, except Drosera, are monotypic and sometimes have been placed in separate families for various reasons. F. Rivadavia et al. (2003) indicated that Droseraceae are monophyletic including these three genera but excluding Drosophyllum; K. M. Cameron et al. (2002) believed that the Old World Aldrovanda is more closely related to Dionaea, and both genera are relicts of a more widespread distribution based on fossil pollen records.

Some species of Droseraceae are grown worldwide as ornamental bog garden or terrarium specimens and as such have been given formal or informal cultivar names. Species of Drosera have been artificially hybridized for horticultural purposes; in the wild the rare hybrids that do occur are normally sterile.

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

Key

1. Leaf blades filiform, not differentiated from petioles; stem base bulbose-cormose (from expanded petiole base); petals 7–17(–20) mm	→ 2
1. Leaf blades linear or suborbiculate to obovate, elongate-spatulate, or cuneate, usually differentiated from petioles; stem base not bulbose-cormose; petals 3–7(–8) mm	→ 3
2. Petals 7–10(–12) mm; leaf blades 8–25(–30) cm × 1 mm, glandular trichomes red to reddish purple, drying dark brown; scapes 6–26 cm.	D. filiformis
2. Petals 12–17(–20) mm; leaf blades 30–50 cm × 1–2 mm, glandular trichomes pale green, drying pale greenish brown; scapes 25–60 cm.	D. tracyi
3. Scapes stipitate-glandular; stipules absent or reduced to minute hairs; seeds black, crateriform.	D. brevifolia
3. Scapes glabrous; stipules present; seeds reddish brown, light brown, brown, or black, striate, areolate, papillose, crateriform, or ridged	→ 4
4. Leaf blades suborbiculate, (broader than long); seeds finely longitudinally striate.	D. rotundifolia
4. Leaf blades linear, orbiculate, or spatulate to obovate or elongate-spatulate (longer than broad); seeds areolate, crateriform, or papillose	→ 5
5. Stipules adnate to petioles	→ 6
5. Stipules free from petioles or essentially so	→ 7
6. Leaf blades obovate to elongate-spatulate; seeds fusiform, striate-areolate, 1–1.5 mm.	D. anglica
6. Leaf blades linear; seeds rhomboidal or oblong-obovoid, crateriform, 0.5–0.8 mm.	D. linearis
7. Plants always rosulate; petioles flat, sparsely glandular-pilose; petals usually pink, 6–7 mm; seeds coarsely papillose-corrugated, 0.4–0.5 mm.	D. capillaris
7. Plants rosulate when young, developing leafy stems 1–8(–20) cm; petioles filiform, glabrous; petals white, 3–6 mm; seeds uniformly papillose, 0.7–1 mm.	D. intermedia

1. Leaf blades of 2 subreniform, hinged lobes that act as jawlike traps, adaxial surface with 3 trigger hairs; inflorescences umbel-like cymes; stamens 15–20.	Dionaea
1. Leaf blades unlobed, surfaces covered with glandular trichomes; inflorescences circinate or scorpioid cymes; stamens 5.	Drosera

Source

FNA vol. 6, p. 420.

FNA vol. 6, p. 418. Author: T. Lawrence Mellichamp.

Parent taxa

Droseraceae

Subordinate taxa