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

896 POACEAE/DICHANTHELIUM
glabrous except for nodes, summits of leaf sheaths, and margins of leaf blades near base; nodes
glabrous or bearded with long spreading hairs; ligule absent or � 1 mm long; leaf blades usually
3–10(–15) mm wide; spikelets 1.5–2.4(–2.6) mm long. Often in low sandy woods, moist, or
often boggy areas, less commonly in drier habitats; widespread in the e 1/2 of TX; se Canada
and e 1/2 of the U.S. w to MI and TX, also AZ, CA, and OR. Apr–Jun, also late summer–fall.
Dichanthelium dichotomum and its relatives comprise one of the most confusing species complexes
known. Countless different approaches have been taken regarding their taxonomy, with
the numerous intergrading morphological entities variously treated as varieties, subspecies, or
distinct species, or not formally recognized (e.g., Diggs et al. 1999). Jones et al. (1997) and Hatch
(2002) recognized five infraspecific taxa in TX, one of which is here treated as a separate species
(D. tenue). Based on work by LeBlond (2001) and Freckmann and Lelong (2003a), we are
tentatively recognizing six for the state. While we are following Freckmann and Lelong (2003a)
in recognizing these taxa as subspecies, we would prefer to treat them at the varietal level as
partially done by LeBlond (2001)—see Turner and Nesom (2000) for an explanation of infraspecific
ranks. However, this would necessitate making new combinations which we cannot justify
without a thorough study of the entire group. The following key to subspecies is slightly modified
from Freckmann and Lelong (2003) and LeBlond (2001). However, there is substantial intergradation
between these subspecies and difficulty should be anticipated when trying to
separate them. The fruits are reportedly dispersed by ants, which are apparently attracted to a
substance (possibly an oil) found under the first glume (Gaddy 1986).
1. Lower nodes hairy.
2. Spikelets 1.5–1.8 mm long; upper floret 0.6–0.8 mm wide ________________________ subsp. microcarpon
2. Spikelets usually 1.8–2.5 mm long; upper floret 0.7–1 mm wide.
3. Spikelets usually glabrous; midculm leaf blades usually 5–7 mm wide ____________ subsp. dichotomum
3. Spikelets pubescent; midculm leaf blades usually 7–14 mm wide ___________________ subsp. nitidum
1. Lower nodes glabrous.
4. Larger leaf blades more than (7–)10 mm wide; leaf sheaths often with pale glandular spots
between the prominent veins; spikelets 1.9–2.6 mm long, acute to beaked ___________ subsp. yadkinense
4. Larger leaf blades less than 10 mm wide; leaf sheaths without glandular spots; spikelets 1.5–
2.3 mm long, obtuse to subacute.
5. Culms weak, ultimately reclining or sprawling over other plants, often flattened ________ subsp. lucidum
5. Culms erect, terete.
6. Leaf blades usually ascending or erect; spikelets broadly ellipsoid or obovoid, 1.5–1.8
(–2.1) mm long, often purplish at the base; plants of wet pine savannahs and open
swamps ____________________________________________________________ subsp. roanokense
6. Leaf blades usually spreading; spikelets ellipsoid, 1.8–2.3 mm long, rarely purplish at the
base; plants of wet-mesic to dry woods and thickets _______________________ subsp. dichotomum
subsp. dichotomum. Wet-mesic to dry, well-drained woodland sites, sandy soils; Henderson, Leon,
and Limestone (BRIT) cos.; Hatch et al. (1990) cited regions 1, 2, 3, 4, and 5; se Canada and e 1/2 of
the U.S. w to MI and TX. [Panicum barbulatum Michx., Panicum dichotomum L., Panicum
dichotomum var. barbulatum (Michx.) A.W. Wood] This is a quite variable taxon (LeBlond 2001).
subsp. lucidum (Ashe) Freckmann & Lelong, (bright, shining, clear). Wet woods and other wet
areas; Leon, Newton, Robertson, Rusk, and San Jacinto (TAES—annotated by S. Hatch) cos.;
mainly se US from NJ s to FL w to TX. [D. lucidum (Ashe) LeBlond, Panicum dichotomum var.
lucidum (Ashe) Lelong, Panicum lucidum Ashe] LeBlond (2001) recognized this taxon as a distinct
species and noted that “the densely papillose fertile lemma and palea readily separate” it
from all other members of the D. dichotomum complex.
subsp. microcarpon (Muhl. ex Elliott) Freckmann & Lelong, (small-fruited). Low or wet woods;
Bowie, Camp, Cass, Hardin, Harrison, Houston, Jasper (BRIT), Angelina, Brazos, Leon, Liberty,
Nacogdoches, Newton, Polk, Robertson, Rusk, Shelby, Smith (TAES—annotated by S. Hatch),