GrassBase - The Online World Grass Flora


W.D. Clayton, M. Vorontsova, K.T. Harman & H. Williamson

© Copyright The Board of Trustees, Royal Botanic Gardens, Kew.

Aristida petersonii

HABIT Perennial; caespitose. Culms erect; 50–100 cm long. Culm-internodes terete; striate; distally glabrous. Lateral branches lacking. Leaf-sheaths mostly shorter than adjacent culm internode; without keel; striately veined; woolly. Ligule a fringe of hairs; 0.3–0.5 mm long. Leaf-blades flat, or conduplicate; 15–30 cm long; 2–2.5 mm wide. Leaf-blade surface glabrous. Leaf-blade margins cartilaginous.

INFLORESCENCE Inflorescence a panicle.

Panicle contracted; linear; 20–30 cm long. Primary panicle branches appressed; 1–2 -nate; 6–12 cm long; bearing 4–8 fertile spikelets on each lower branch.

Spikelets solitary. Fertile spikelets pedicelled.

FERTILE SPIKELETS Spikelets comprising 1 fertile florets; without rhachilla extension. Spikelets linear; subterete; 9–13 mm long; breaking up at maturity; disarticulating below each fertile floret. Floret callus evident; 5 mm long; pubescent.

GLUMES Glumes similar; exceeding apex of florets; thinner than fertile lemma. Lower glume lanceolate; 9–13 mm long; 1.5–2 length of upper glume; membranous; light brown, or purple; 1 -veined. Lower glume lateral veins absent. Upper glume lanceolate; 6–7 mm long; 1.7–2 length of adjacent fertile lemma; membranous; light brown, or purple; 1 -veined. Upper glume lateral veins absent. Upper glume apex acuminate.

FLORETS Fertile lemma linear; subterete; 3–4 mm long; coriaceous; without keel; 3 -veined. Lemma surface glabrous. Lemma margins convolute; covering most of palea. Lemma apex awned; 1 -awned, or 3 -awned. Principal lemma awn geniculate, or 3-branched; with 7–9 mm long limb; with twisted column. Column of lemma awn 4–6 mm long. Lateral lemma awns 0.1 mm long; shorter than principal. Palea 1–1.5 mm long; hyaline; 2-keeled.

FLOWER Lodicules 2; 1–1.5 mm long. Anthers 3.

FRUIT Caryopsis with adherent pericarp; fusiform; 4.5–5.5 mm long; dark brown.

DISTRIBUTION North America: Mexico.

NOTES Aristideae. Allred et al 2004.

Please cite this publication as detailed in How to Cite Version: 3rd February 2016.