| James P. Smith, Jr. |
Plants usually perennial; often cespitose
in appearance, rhizomatous. Culms 10-100 cm, erect to decumbent, simple
or sparingly branched. Leaves cauline, evidently distichous; sheaths
often strongly overlapping; auricles absent; ligules 0.1-0.5 mm,
membranous, ciliate; blades linear to ovate-lanceolate, lacking midribs.
Inflorescences terminal, panicles of spikelike branches, these subdigitately
or racemosely arranged, usually strongly divergent to reflexed, sometimes naked
basally, spikelets borne singly. Spikelets widely spaced to slightly imbricate,
appressed to the branches, shortly pedicellate, laterally compressed, with 1-2(4)
florets, only the lowest 1(2) floret(s) bisexual; rachilla extensions present,
usually with a highly reduced, sterile floret(s); disarticulation above
the glumes, florets falling together. Glumes subequal, usually exceeding
the bisexual florets, narrow, acuminate, 1-veined; lemmas of bisexual florets
3-veined, midveins prominent, apices minutely bidentate, usually awned from between
the teeth, rarely unawned; anthers (2)3. x = 10. Name from Greek
gymnos, naked, and pogon, beard, alluding to the naked prolongation
of the rachilla found in many species.
Gymnopogon, a genus of around 15 species, extends from the United States
to South America, with one additional species ranging from India to Thailand.
Three species are native to the Flora region. Gymnopogon is most
likely to be confused with Chloris, but its species
differ from most species of Chloris in having a more highly reduced, sterile
floret at the end of the rachilla extension and in its distichous leaves.
1 |
Plants with
elongate rhizomes; panicle branches naked for at least 1/3 of their length
..... 1. G. brevifolius |
Plants with short, knotty rhizomes or
cespitose with a knotty base; panicle branches naked for less than 1/3
of their length, often spikelet-bearing to the base (2) |
|
Lemma awns 4-12.2 mm long
..... 2. G. ambiguus |
|
Lemma awns 0-2.2 mm long ..... 3.
G. chapmanianus |
1. Gymnopogon brevifolius Trin.
Shortleaf Skeletongrass
Plants rhizomatous, rhizomes to 9 cm. Culms 10-100 cm, erect or
decumbent, single or in clumps, simple or sparingly branched. Sheaths mostly
glabrous, throats pubescent; collars mostly glabrous, margins often with
hairs; ligules about 0.5 mm; blades (1)2-8 cm long, 2-8(10) mm wide,
glabrous abaxially, glabrous or scabrous adaxially. Panicles 10-30 cm;
branches (6)10-17(20) cm, naked for at least the lower 1/3 of their length,
spikelets distant to remote. Spikelets with 1(2) florets; rachilla extensions
naked or with a minute rudimentary floret. Glumes (2)3.5-5 mm; bisexual
lemmas 1.8-3.8 mm, awns 0.8-3 mm; anthers 3, 0.8-1 mm. Caryopses
1.6-1.9 mm long, 0.3-0.5 mm wide. 2n = unknown.
Gymnopogon brevifolius grows in dry to somewhat moist sandy pine woodlands
of the southeastern United States, usually in loamy soils. It generally has rather
weak, decumbent culms that tend to be obscured by the surrounding vegetation.
Plants with stiffer culms tend to be confused with Gymnopogon
ambiguus, but differ as discussed under G. ambiguus. Intermediate
plants may be hybrids between the two species; there has been no experimental
evaluation of this hypothesis.
2. Gymnopogon ambiguus (Michx.) Britton, Sterns & Poggenb.
Bearded Skeletongrass
Plants cespitose, with a knotty base of short rhizomes. Culms
20-100 cm, suberect to spreading, stiff, simple to sparingly branched. Sheaths
mostly glabrous, throats sometimes pubescent; collars conspicuously pubescent;
ligules about 0.2 mm; blades (1.5)2.5-12 cm long, (2)5-10(18)
mm wide, somewhat cordate at the base, mostly glabrous, often pubescent near
the basal margins. Panicles (6)11.5-30(35) cm; branches (3)7-24
cm, stiffly spreading to somewhat reflexed, spikelet-bearing from the base,
spikelets remote to slightly imbricate. Spikelets with 1(2) florets.
Glumes 4-7 mm; calluses bearded; bisexual lemmas 2.5-5(6)
mm, awns 4-12.2 mm; second florets often reduced to an obliquely inserted
2.4-6.2 mm awn; anthers 3, 0.8-1.2 mm. Caryopses 2-3 mm long,
0.2-0.5 mm wide. 2n = 40.
Gymnopogon ambiguus grows in sandy pine woodlands of the southeastern
United States, Haiti, and the Dominican Republic. It often grows with G.
brevifolius, from which it differs in being more robust, having long,
wider leaves, longer lemma awns, and, usually, having panicle branches that
are spikelet-bearing to the base. Although spikelets of Gymnopogon ambiguus
usually have only one floret, several plants from Texas have been found
in which two florets per spikelet were the norm.
There is an 1853 collection of G. ambiguus supposedly
from Doña Ana County, New Mexico, but there have been no recent collections
from anywhere near there; it is possible that the locality data on the label
are incorrect.
3. Gymnopogon chapmanianus Hitchc.
Chapman's Skeletongrass
Plants usually perennial; cespitose from a knotty base. Culms
20-70 cm, erect to sprawling, simple or sparingly branched from the lower nodes.
Sheaths glabrous; ligules 0.1-0.3 mm; blades 1.3-8.5 cm
long, 2-8 mm wide, glabrous. Panicles 8-23.5 cm; branches 2-15
cm, ascending, widely spreading, or reflexed, spikelet-bearing from the base
or naked for less than 1/3 of their length. Spikelets with (1)2-3(4)
florets. Glumes to 6 mm, sometimes widely divergent; lemmas of bisexual
florets 1.5-2.3 mm, unawned or awned, awns 0.7-2.2 mm; terminal sterile
florets minute, rudimentary, awned, awns not exserted from the spikelets;
anthers 3, 0.5-0.8 mm. Caryopses 1.2-1.5 mm long, 0.3-0.4 mm wide.
2n = unknown.
Gymnopogon chapmanianus grows in sandy pine barrens and sites
inhabited by dwarf palmetto, Serenoa repens. As interpreted here, G.
chapmanianus
includes G. floridanus Swallen. Smith (1971)
treated the two as distinct species, but he acknowledged that they overlapped
morphologically, ecologically, and geographically. Subsequent fieldwork
has not supported the recognition of two entities. Smith's most intriguing
observation was that only plants fitting the G. floridanus end
of the morphological range produced mature caryopses. The reproductive
biology of G. chapmanianus
merits examination.