keys to the vascular plants of east texas - Botanical Research ...

914 POACEAE/DIGITARIA
tinct species. However, we have been unable to find sufficient differences in the material we
have seen to warrant separation at the species level. Because of morphological overlap, we are
therefore following Jones et al. (1997), Yatskievych (1999), and Wipff (2003f) in treating D.
villosa as a variety of D. filiformis. Wipff (2003f) suggested that “Further study may show that
the two varieties should be combined.” We agree that additional study is needed to determine
the appropriate taxonomic rank at which to recognize these entities. The county distribution
map does not distinguish varieties.
1. Spikelets (1.3–)1.5–1.9(–2) mm long; inflorescence branches usually 8–13 cm long; lowermost
leaf sheaths usually sparsely hairy, sometimes densely so; culms 80 cm or less tall _____________ var. filiformis
1. Spikelets 2–2.8 mm long; inflorescence branches usually (10–)13–25 cm long; lowermost leaf
sheaths densely hairy; culms usually 75–130(–150) cm tall _________________________________ var. villosa
var. filiformis. Tufted annual with erect culms usually 50–80 cm tall, similar to var. villosa; 2n = 36
(Gould 1975b). Sandy fields or woods; Gould (1975b), Hatch et al. (1990), and Hatch (2002) cited
the Pineywoods, Post Oak Savannah, and Gulf Prairies and Marshes; however, we have seen few
East TX specimens that fall within this variety; e U.S. from NH s to FL w to IA and TX. Sep–Oct.
var. villosa (Walter) Fernald, (softly hairy), SHAGGY CRAB GRASS. Tufted annual with erect culms
usually 75–130(–150) cm or more tall, much-branched at base; upper glume and lemma of fertile
floret usually more pubescent than in var. filiformis; 2n = 36 (Gould 1975b). Disturbed
sandy soils; widespread in e 1/2 of TX; se U.S. from VA s to FL w to MO, OK, and TX, also IL.
Aug–Nov. [Digitaria villosa (Walter) Pers.]
Digitaria insularis (L.) Mez ex Ekman, (pertaining to or inhabiting an island), SOUR GRASS.
Tufted perennial from a knotty base; culms erect, 35–100(–150) cm tall; leaf blades glabrous or
nearly so; inflorescence usually tan- or buff-tinged due to conspicuous pubescence, the numerous
branches appressed, densely-flowered; terminal pedicel of branches 2–5 mm long; spikelets
3.6–5.9 mm long (excluding hairs); upper glume and lemma of lower floret densely long-hairy,
the hairs 2–4(–6) mm long; 2n = 36 (Gould 1975b). Ditches, moist areas; Bastrop, Bell, Bexar, and
Caldwell (Turner et al. 2003) cos. in sw part of East TX; scattered in TX, but mainly Gulf Prairies
and Marshes and South TX Plains; AZ, FL, and TX. Aug–Nov. [Trichachne nutans (L.) B.R.
Baum, Trichachne insularis (L.) Nees]
Digitaria ischaemum (Schreb.) Muhl., (Greek: ischaemos, blood-restraining, from supposed styptic
properties), SMOOTH CRAB GRASS. Tufted annual to ca. 50(–70) cm tall; leaf sheaths and blades
usually glabrous or with sparse pubescence; inflorescence digitately arranged or nearly so
(there can be a short main axis), the branches usually ca. 3–9(–11+) cm long; spikelets (1.7–)1.9–
2.3 mm long; upper glume more than 3/4 as long as lemma of upper floret; 2n = 36 (Gould 1975b).
Open woods, waste places; scattered in East TX w to Leon Co. (Turner et al. 2003); also n Gulf
Prairies and Marshes; s Canada and nearly throughout the U.S. Aug–Nov. Native of Eurasia I
Digitaria patens (Swallen) Henrard, (spreading, opening out), TEXAS COTTON-TOP. Tufted perennial
similar to D. californica, but distinguished as in the key to species; culms 40–90 cm tall;
inflorescence branches 4–10, stiffly spreading, the inflorescence open; spikelets widely-spaced,
many of them not overlapping or only slightly so; lemma of sterile, lower floret usually with
hairs ca. 2 mm or less long; 2n = 72 (Gould 1975b). Brushy areas, pastures, often in disturbed habitats,
well-drained, usually sandy soils; Bexar and Caldwell (Turner et al. 2003) cos. on sw margin
of East TX; mainly s Gulf Prairies and Marshes and South TX Plains, also e Edwards Plateau; endemic
to TX and adjacent Mexico (Wipff 2003f). May–Nov. [Trichachne patens Swallen] Gould
(1975b) indicated that this species “appears to be an octoploid derivative of D. californica.”
Digitaria sanguinalis (L.) Scop., (of blood-red color, possibly due to the sometimes gray-brown to
purple spikelets), HAIRY CRAB GRASS, LARGE CRAB GRASS. Annual similar to D. ciliaris but with