17.41   GYMNOPOGON P. Beauv.
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.


SELECTED REFERENCE Smith, J.P., Jr.1971. Taxonomic revision of the genus Gymnopogon (Gramineae). Iowa State Coll. J. Sci. 45:319-385.

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)
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.