13.015   HOLCUS L.

DRAFT TREATMENT. Please send comments to Mary Barkworth.
Lisa A. Standley

Plants usually perennial, rarely annual; cespitose or rhizomatous, rarely both cespitose and rhizomatous. Culms (8)20-200 cm, glabrous or pubescent; nodes glabrous or retrorsely pubescent. Sheaths open; auricles absent; ligules 1-5 mm, membranous, entire or erose-ciliate, glabrous or puberulent; blades flat, pubescent. Inflorescences terminal panicles, contracted to open. Spikelets laterally compressed, with 2(3) florets, lower florets bisexual, upper floret(s) staminate or sterile; rachillas curved below the lowest florets, sometimes prolonged beyond the uppermost florets; disarticulation below the glumes. Glumes equaling to exceeding the florets, strongly keeled; lower glumes 1-veined; upper glumes 3-veined; calluses glabrous or pubescent; lemmas firm, shining, glabrous or pubescent, obscurely 3-5-veined, often bidentate; lower lemmas unawned; upper lemmas awned from below the apices, awns hooked or geniculate; paleas thin, subequal to the lemmas; lodicules 2, glabrous, toothed or not toothed; anthers 3; ovaries glabrous. Caryopses glabrous. x = 4, 7. Name from the Greek holkos, a kind of grain, perhaps sorghum.

Holcus, a genus of eight species, is native to Europe, North Africa, and the Middle East. One species, Holcus lanatus, has become widely naturalized in the Americas, Japan, and Hawaii; a second, Holcus mollis, has become a troublesome weed in some areas of the Flora region.


SELECTED REFERENCES Carroll, C.P. and K. Jones. 1962. Cytotaxonomic studies in Holcus. III. A morphological study of the triploid F1 hybrid between H. lanatus L. and H. mollis L. New Phytol. 61:72-84; Jones, K. 1958. Cytotaxonomic studies in Holcus L. I. The chromosome complex in Holcus mollis L. New Phytol. 57:191-210; Jones, K. and C.P. Carroll. 1962. Cytotaxonomic studies in Holcus L. II. Morphological relationships in H. mollis L. New Phytol. 6163-71; Zandee, M. and P.C.G. Glas. 1982. Studies in the Holcus lanatus-Holcus mollis complex (Poaceae [= Gramineae]). Proc. Kon. Ned. Akad. Wetensch., C 85:413-437.

1
Awns 1-2 mm long, forming a curved hook at maturity; culms densely soft-pubescent adjacent to the lower nodes; plants cespitose, without rhizomes ..... 1. H. lanatus
Awns 3-5 mm long, straight or geniculate at maturity; culms glabrous or sparsely pubescent adjacent to the lower nodes; plants not cespitose, rhizomatous ..... 2. H. mollis


1.   Holcus lanatus L.
Velvetgrass, Yorkshire Fog, Houlque Laineuse

Plants perennial; cespitose, not rhizomatous. Culms 20-100 cm, erect, sometimes decumbent; lower internodes densely pilose, with hairs to 1 mm; uppermost internode often glabrous. Sheaths densely pubescent; ligules 1-4 mm, truncate, erose-ciliolate; blades 2-20 cm long, (3)5-10 mm wide, densely soft-pubescent. Panicles 3-15(20) cm long, 1-8 cm wide; branches hirsute; pedicels 0.2-1.6(4) mm, pilose, hairs to 0.3 mm. Spikelets 3-6 mm; rachillas 0.4-0.5 mm, glabrous. Glumes exceeding and enclosing the florets, membranous, ciliate on the keels and veins, usually scabrous, puberulent, or villous between the veins, especially towards the apices, whitish-green, often purple over the veins and towards the apices; lower glumes lanceolate, narrow, acute; upper glumes ovate, wider and longer than the lower glumes, midveins often prolonged as an awn to 1.5 mm, apices obtuse, somewhat bifid; calluses sparsely hirsute; lemmas 1.7-2.5 mm, acute, erose-ciliate; upper lemmas shallowly bifid, awns 1-2 mm, often purple-tipped, slightly twisted and strongly hooked at maturity; anthers (1.2)2-2.5 mm. 2n = 14.

Holcus lanatus grows in disturbed sites, moist waste places, lawns, and pastures, in a wide range of edaphic conditions and at elevations from 0-2300 m. A native of Europe, it was widely distributed in North America by 1800. It is an ancestor of the polyploid complex represented by Holcus mollis. In Europe, it hybridizes with tetraploids of H. mollis to form a sterile triploid that spreads vegetatively.


2.   Holcus mollis L.
Creeping Velvetgrass, Houlque Molle

Plants perennial; not cespitose, rhizomatous, rhizomes to 40 cm. Culms 20-100(150) cm, usually decumbent at the base; lower internodes glabrous or sparsely pubescent. Sheaths glabrous or hirsute; ligules 1-5 mm, obtuse, erose; blades 2-20 cm long, 3-10 mm wide, pubescent. Panicles 4-20(22) cm long, to 3 cm wide; branches puberulent or ciliate; pedicels to 5 mm long, pilose, hairs to 0.3 mm. Spikelets 4-6(7) mm; rachillas hairy. Glumes exceeding and enclosing the florets, subequal, nearly the same width, ovate, membranous, whitish-green when young, straw-colored with age, veins ciliate, often purple, intercostal regions scabrous or glabrous, apices acuminate or acute, unawned; calluses densely to sparsely hirsute; lemmas 2-2.5 mm, glabrous, acute; upper lemmas bifid, awned above midlength, awns 3-5 mm, scabrous, straight or geniculate at maturity; anthers about 2 mm. 2n = 28 (35, 42, 49).

Holcus mollis grows in moist soil and disturbed sites, including lawns and damp pastures. It is a European introduction that has persisted in the Flora region, becoming a problematic weed in ungrazed pastures, prairie remnants, and oak savannahs in portions of the Pacific Northwest. It is also sold as an ornamental. There are two subspecies: Holcus mollis L. subsp. mollis (stems not thickened and tuberous at the base; panicles lax, brownish or purplish) and H. mollis subsp. reuteri (Boiss.) Malag. (stems thickened and tuberous at the base; panicles narrow, whitish). North American introductions belong to subsp. mollis.