Drosera
Drosera filiformis
catch-fly, dew-threads, droséra, rossolis, sundew
dew-threads, thread-leaf sundew
erect;
stipules adnate to petioles for entire length, 10 mm, margins fimbriate, forming woolly appearance of cormose base;
petiole not differentiated from blade;
blade filiform, 8–25(–30) cm × 1 mm, surfaces glandular-hairy, trichomes red to reddish purple, drying dark brown.
4–12(–24)-flowered;
scapes 6–26 cm, glabrous.
glandular-pilose.
10–20 mm diam.;
sepals connate basally, oblong to elliptic, 4–7 × 2–2.5 mm, glandular-pilose;
petals pink to purple-lavender, broadly ovate, 7–10(–12) × 5–15 mm, apical margins erose.
obovoid, splitting between placentae.
5–6 mm.
20–70, minute.
black, ellipsoid, abruptly caudate at both ends, 0.5–0.8 mm, coarsely crateriform, pits in 16–20 lines.
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.
= 10.
= 20.
Drosera
Drosera filiformis
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 filiformis is disjunct in the outer Coastal Plain, from Nova Scotia and Connecticut to Maryland, southeastern North Carolina, and Bay and Washington counties, Florida. The species has been reported from South Carolina, but no specimens from there have been seen. It is introduced in Caroline County, Virginia, and Preston County, West Virginia, and possibly other localities peripheral to its range; it is short-lived in some localities. B. A. Sorrie (1998b) gave a detailed account of the distribution and habitats of D. filiformis as well as convincing evidence that D. tracyi is a distinct species.
The species is very easy to cultivate, and the cormose-based clumps multiply and may be divided while dormant.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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 |
CA
OR
WA
Flora NW
PNW Herbaria
WildflowerSearch
iNaturalist
USDA Plants Database
Go Botany
MD Biodiversity
