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Descriptions

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

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

Tristachya laxa

HABIT Perennial; caespitose. Culms erect; 150–200 cm long. Leaf-sheaths pubescent. Ligule a fringe of hairs. Leaf-blades conduplicate, or convolute; 40–70 cm long; 5–10 mm wide. Leaf-blade surface scabrous; rough adaxially. Leaf-blade margins scabrous.

INFLORESCENCE Inflorescence a panicle; embraced at base by subtending leaf.

Panicle open; ovate; effuse; 40–50 cm long. Primary panicle branches drooping; simple, or sparsely divided; 10–20 cm long. Panicle branches capillary; pubescent in axils.

Spikelets in threes. Fertile spikelets pedicelled; 3 in the cluster. Pedicels free; subequal; 1.5–2.5 mm long.

FERTILE SPIKELETS Spikelets comprising 1 basal sterile florets; 1 fertile florets; without rhachilla extension. Spikelets lanceolate; laterally compressed; compressed slightly; 15–20 mm long; breaking up at maturity; disarticulating below each fertile floret. Floret callus elongated; pubescent; pungent.

GLUMES Glumes persistent; dissimilar; exceeding apex of florets. Lower glume lanceolate; 13–18 mm long; 0.9 length of spikelet; chartaceous; dark brown; without keels; 3 -veined. Lower glume primary vein scabrous. Lower glume surface glabrous. Lower glume apex acute. Upper glume lanceolate; 1 length of spikelet; chartaceous; without keels; 3 -veined. Upper glume primary vein scabrous. Upper glume surface glabrous. Upper glume apex obtuse.

FLORETS Basal sterile florets male; with palea; separately deciduous. Lemma of lower sterile floret similar to upper glume; lanceolate; 1 length of spikelet; chartaceous; 5–7 -veined; acute. Fertile lemma oblong; 8–9 mm long; coriaceous; without keel; 9 -veined. Lemma surface pubescent. Lemma margins involute; interlocking with palea keels. Lemma apex lobed; 2 -fid; with lanceolate lobes; with lobes 2 mm long; awned; 1 -awned. Principal lemma awn from a sinus; geniculate; subterete below; 20–25 mm long overall; with twisted column; deciduous; abscissing from top of lemma. Palea 2 -veined. Palea keels approximate; thickened; winged; narrowly winged.

FLOWER Anthers 3.

FRUIT Caryopsis with adherent pericarp.

DISTRIBUTION North America: Mexico.

NOTES Arundinelleae. Scribn & Merr 1992.

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