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Vahl's fimbristylis, Vahl's fimbry

fork fimbry

Habit Plants annual, cespitose, delicate, 4–15 cm, bases soft; rhizomes absent. Plants perennial, cespitose, (10–) 20–80 cm, base thickened, not bulbous; rhizomes absent.
Leaves

polystichous, mostly spreading or excurved, often exceeding culms;

sheaths entire, abaxially smooth or sparsely hirtellous;

ligule absent;

blades filiform, to 0.5 mm wide, somewhat involute, abaxially glabrous or ascending-strigillose.

nearly distichous, spreading to ascending, 1/2 length of culms;

sheaths distally ciliate, backs mostly glabrous;

ligule line of short hairs;

blades narrowly linear, 2–3 mm wide, flat to broadly involute, scabridciliate, adaxially smooth or hirtellous.

Inflorescences

terminal;

spikelets sessile or subsessile in single capitate leafy-involucrate cluster;

scapes filiform;

involucral bracts leafy, setaceous, greatly overtopping inflorescence.

anthelae compound, dense or open, ascending-branched, longer than broad;

scapes slender, 1 mm wide, slightly compressed distally;

proximalmost involucral bract exceeding anthela.

Spikelets

greenish, cylindric to lanceoloid-cylindric, 5–10 mm;

fertile scales narrowly ovate to lanceolate, 1–1.5 mm, acute, glabrous, midrib strong, excurrent as cusp.

pale drab brown to chestnut brown, ovoid-lanceoloid, 4–8 mm;

fertile scales broadly oblong or ovate, 2 mm, acute to obtuse angled, glabrous, midrib reaching scale tip or excurrent, finely mucronate.

Flowers

stamens 1;

styles 2-fid, slender, bulbous-based, smooth or papillate.

stamens 1–2;

styles 2-fid, flat, fimbriate.

Achenes

pale, tumidly obovoid, 0.5–0.7 mm, cancellate, pits horizontally rectangular in 5–7 vertical rows per side.

white to brownish, lenticular, obovoid, 1–1.2 mm, cancellate, each face longitudinally with (5–)10–12 ribs, connected by vertical rows of horizontally rectangular pits.

2n

= 20.

= 20, 30.

Fimbristylis vahlii

Fimbristylis dichotoma

Phenology Fruiting summer–fall. Fruiting summer–fall, into winter southward.
Habitat Moist to wet, alluvial or mineralized banks, shores, fluctuating pond and lake edges, often a “drawdown” plant around stock tanks and reservoirs Moist, usually sandy waste areas, roadsides, low fields, and savannas
Elevation 0–500 m (0–1600 ft) 0–200 m (to 2000 m, tropics) (0–700 ft (to 6600 ft, tropics))
Distribution
from FNA
AL; AR; AZ; CA; FL; GA; IL; KS; KY; LA; MO; MS; NE; OK; SC; TN; TX; Mexico; Central America; South America
[WildflowerSearch map]
[BONAP county map]
from FNA
AL; FL; GA; LA; MS; NC; SC; TX; Mexico; Central America; South America; Atlantic Islands; Pacific Islands; Indian Ocean Islands; West Indies; Africa; Eurasia; Bermuda; Australia [Introduced in North America]
[WildflowerSearch map]
[BONAP county map]
Discussion

Fimbristylis dichotoma is found in temperate to tropical regions worldwide. It is one of the most widespread and weedy species of Fimbristylis, unquestionably with many races and forms. The two commonest forms in the United States often occur in mixed populations, one sort with inflorescence branches more ascending, inflorescence dense, habit lower, and leaves broader; the other sort usually taller, inflorescence more sparse, branches more widely spreading, and leaves more ascending and narrower. The abundance of such plants both in regions where rice originated and in regions where rice is, or was, introduced, indicates an Asian origin for such weeds.

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

Source FNA vol. 23, p. 127. FNA vol. 23, p. 125.
Parent taxa Cyperaceae > Fimbristylis Cyperaceae > Fimbristylis
Sibling taxa
F. annua, F. autumnalis, F. brevivaginata, F. caroliniana, F. castanea, F. cymosa, F. decipiens, F. dichotoma, F. miliacea, F. perpusilla, F. puberula, F. schoenoides, F. squarrosa, F. thermalis, F. tomentosa
F. annua, F. autumnalis, F. brevivaginata, F. caroliniana, F. castanea, F. cymosa, F. decipiens, F. miliacea, F. perpusilla, F. puberula, F. schoenoides, F. squarrosa, F. thermalis, F. tomentosa, F. vahlii
Synonyms Scirpus vahlii, F. apus, F. congesta, F. vincentii, Isolepis vahlii, Scirpus apus Scirpus dichotomus, F. annua var. diphylla, F. brizoides, F. diphylla subsp. diffusa, F. glauca, F. polymorpha, Scirpus diphyllus
Name authority (Lamarck) Link: Hort. Berol. 1: 287. (1827) (Linnaeus) Vahl: Enum. Pl. 2: 287. (1805)
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