26.20   HETEROPOGON Pers.
Mary E. Barkworth

Corrected June 29, 2009.

Plants annual or perennial; cespitose. Culms 20-200 cm, simple or branched. Leaves sometimes aromatic and smelling of lemon oil or citronella; sheaths keeled, sometimes with a row of glandular depressions on the keel; ligules membranous, glabrous or ciliate. Inflorescences terminal and axillary; peduncles usually with 1 rame, sometimes with several in a digitate cluster; rames with 3-10 homogamous, unawned, sessile-pedicellate spikelet pairs on the lower 1/4-2/3 and heterogamous, awned, sessile-pedicellate spikelet pairs distally, axes slender, without a translucent median groove; disarticulation in the rames, beneath the sessile spikelets of the heterogamous spikelet pairs, sometimes also below their pedicellate spikelets. Homogamous spikelet units sterile or staminate; calluses poorly developed; glumes membranous, many-veined, keels winged above. Heterogamous spikelet units: sessile spikelets bisexual, terete; calluses 1.5-3 mm, sharp, antrorsely strigose, hairs golden brown; glumes coriaceous, pubescent, concealing the florets; lower glumes enclosing the upper glumes, obscurely 5-9-veined; upper glumes sulcate, 3-veined; lower florets sterile, reduced to a hyaline lemma; upper florets bisexual, lemmas with conspicuous, geniculate awns; awns 5-15 cm, with hairs. Caryopses lanceolate, sulcate on 1 side. Pedicels short, free of the rame axes, not grooved; pedicellate spikelets sterile or staminate, larger than the sessile spikelets; calluses long, glabrous, functioning as pedicels; glumes membranous, many-veined, keels winged above. x = 10, 11. Name from the Greek heteros, different, and pogon, beard, alluding to the difference between the calluses of the spikelets in the heterogamous pairs.

Heteropogon is a pantropical genus of eight to ten species. One species is native to the Flora region and one is introduced. Many grow well on poor soils.

Selected Reference: Betancourt, J. L., Devender, T. R. V. and Martin, P. S., editors. 1990. Packrat middens: The last 40,000 years of biotic change. University of Arizona Press, Tucson, AZ.



1
Glumes of the pedicellate spikelets of the heterogamous spikelet units without glandular pits; plants perennial ..... 1. H. contortus
Glumes of the pedicellate spikelets of the heterogamous spikelet units with a row of glandular pits along the midvein; plants annual ..... 2. H. melanocarpus


1.   Heteropogon contortus (L.) P. Beauv. ex Roem. & Schult.
Tanglehead

Plants perennial. Culms 20-150 cm, erect. Sheaths smooth, reddish; ligules 0.5-0.8 mm, cilia 0.2-0.5 mm; blades 10-15 cm long, 2-7 mm wide, flat or folded, glabrous or pubescent. Rames 3-7 cm, secund, with 12-22, brown to reddish-brown, sessile-pedicellate spikelet pairs. Homogamous spikelets 6-10 mm. Heterogamous spikelets: sessile spikelets 5-10 mm, brown, awned; calluses 1.8-2 mm, strigose; awns 6-10 cm; pedicellate spikelets 6-10 mm, unawned; glumes ovate-lanceolate, glabrous or with papillose-based hairs distally, without glandular pits, greenish to purplish-brown, becoming stramineous when dry. 2n = 40, 50, 60.

Heteropogon contortus grows on rocky hills and canyons in the southern United States, occupying a variety of different habitats, including disturbed habitats. It is is now found in tropical and subtropical areas throughout the world. CORRECTION: The printed volume states that H. contortus is probably native to eastern Asia, but its seeds have been found in packrat middens, demonstrating that it is native to North America. I thank David Smith for bringing this error to my attention and Juloa Betancourt and Chris Best for locating the reference.

Heteropogon contortus is a valuable forage grass if continuously grazed so as to prevent the calluses from developing. It is also considered a weed, being able to establish itself in newly disturbed and poor soils.


2.   Heteropogon melanocarpus (Elliott) Benth.
Sweet Tanglehead

Plants annual. Culms 50-200 cm, often with prop roots, freely branching above the base. Sheaths glabrous, with a row of glandular depressions along the keel; ligules 2-4 mm, erose to lacerate, glabrous; blades 30-50 cm long, 3-12 mm wide, usually folded, abaxial surfaces with dark glandular depressions along the keel, adaxial surfaces with scattered papillose-based hairs near the base, scabrous elsewhere. Rames 2.5-6.5 cm. Homogamous spikelets 10-14 mm, green; lower glumes glabrous, unawned. Heterogamous spikelets: sessile spikelets 8-11.5 mm, dark brown, awned; calluses about 3 mm; awns 10-15 cm; pedicellate spikelets 16-21 mm, unawned; lower glumes scabrous or sparsely ciliate distally, midveins glandular, pitted. 2n = 20.

Heteropogon melanocarpus is probably native to the Eastern Hemisphere, but is now found in tropical regions throughout the world. It grows in pine woods, fields, and disturbed areas of the southern United States. When fresh, plants of H. melanocarpus smell like citronella oil.