Drosera filiformis

BOTANICAL NAMES: Drosera filiformis Raf. Two forms or varieties are also generally recognized within the species: D. filiformis v. filiformis Raf. (also known as D. filiformis v. typica Wynne) and D. filiformis v. tracyi (Macfar.) Diels.

COMMON NAMES: Threadleaf sundew, dew-thread. RANGE: As a species, from Cape Cod along the coastal plain into southern Mississippi.


TRAP SEASON: Spring and summer. Forms hibernacula.

DESCRIPTION-The leaves are erect with short petioles and filiform gland-bearing leaf blades. In D. filiformis v. filiformis (typica), the leaf blades measure to 25 cm and have bright red to purple glands; in D. filiformis v. tracyi they measure up to 50 cm and are uniformly green. The hibernacula of v. filiformis (typica) are by far the more hirsute. The flowers, which are always rose pink, are the largest of any variety of Drosera and are borne on tall scapes.

There are some floral differences between the varieties. The flowers of v. filiformis (typica) measure up to 1.5 cm across, and the outer margins of the petals are smooth. On observing the flower with a hand lens, one will note that the two anther lobes are joined at the tip and that the stamen filament is pale red. In v. tracyi, the flower is even larger, up to 2 cm across, and the petals frequently have somewhat scalloped outside margins. The larger anther lobes are separate, and the stamen filament is green.

GENERAL. - This is our largest sundew, and a stand of them growing in a savannah or on the margin of a bog is truly an impressive sight, especially on a dewy morning with the sun shining through the plants.

The smaller, red form occurs from Cape Cod south into the New Jersey Pine Barrens, where it is plentiful, and it is found in disjunct locations in the eastern Carolinas, Georgia, and a recently described location

Fig. 5-9. D. filiformis v. tracyi. A stand of the plants in a closely cropped savannah, the glow caused by the early morning sun striking their glandular leaves.

Fig. 5-10. D. filiformis v. tracyi, a single plant. The color is diffusely pale green.

Fig. 5-11. Leaves of the two varieties of D. filiformis, v. tracyi being pale green and v. filiformis (typica) having red glands.

in northern Florida. The larger, green form grows in the southern Gulf coastal area, where it is very common. The ranges of the two forms reportedly overlap in South Carolina. In spite of this small area of sym-patry, the two forms have not been found in the same stand, and a natural hybrid is not reported, although hybrids have been produced in the greenhouse.

As you will have noted, there is a minor problem

Fig. 5-12. D. filiformis v. filiformis (typica). A stand of the species in eastern North Carolina. This variety has a red cast, which can be appreciated even at this distance.

Fig. 5-13. D. filiformis v. filiformis (typica), a single plant in the New Jersey Pine Barrens. The glandular character of the leaves is clear, and they are generally reddish.

Fig. 5-14. Flowers of D. filiformis v. filiformis (typica).

These are always rose pink, and the species has the largest flowers of any Drosera in North America.

Fig. 5-15. A hibernaculum of D. filiformis v. filiformis (typica) just breaking in the early spring.

Fig. 5-15. A hibernaculum of D. filiformis v. filiformis (typica) just breaking in the early spring.

of nomenclature with these varieties or forms. The original name, D. filiformis, referred mainly to the smaller, red plants. Then, the larger green plants were considered by one botanist to be different enough to warrant designation as a separate species, and they were named D. tracyi. However, over the years, a majority of botanists have agreed that both plants are subspecific forms of the same species, so a varietal designation has been used, and the larger, green, southern plant has become known as v. tracyi. A second problem arose, however, in the reclassification of the northern, red plant. The first record of any varietal designation is by Frances Wynne, who in 1944 formally described v. typica as a new variety. There is no further reference until 1960, when Carroll Wood casually mentioned v. filiformis when referring to the northern, red form. By the usual rules of precedence, Wynne's designation, which was formally described first, should be official unless properly changed; but somehow Wood made an undescribed nomenclatural leap to v. filiformis, which has gained slightly more popular use. I can find no reference to a formal description of the v. filiformis designation in the 1960 paper written by Wood, who is usually meticulous in this respect, nor did Wood make a formal re description or offer reasoning at that time. He may be applying a newer taxonomic procedure whereby the first of several subspecies, forms, or varieties of a species bears the specific epithet.

As a rule, this species prefers a slightly drier habitat than do most other species of Drosera, and it is more often found in peaty, sandy soils than in sphagnum. D. filiformis is easily found in proper locations, except in areas where it may be partly obscured by surrounding grass and sedges. In these cases, one will have to make a close examination to distinguish the dewy threadleaf from a blade of grass.

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