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Descriptions

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

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

Tripsacum laxum

HABIT Perennial. Butt sheaths pilose. Culms erect; robust; 300–500 cm long; 5–10 mm diam. Leaves cauline. Leaf-sheaths glabrous on surface. Ligule a ciliolate membrane. Leaf-blades 40–80 cm long; 30–70 mm wide. Leaf-blade surface glabrous. Leaf-blade apex acuminate.

INFLORESCENCE Monoecious; with male and female spikelets in the same inflorescence. Inflorescence composed of racemes; terminal and axillary. Peduncle glabrous.

Racemes 12–23; digitate; drooping; arcuate; smoothly terete; unilateral; 10–20 cm long. Central inflorescence axis 4–10 cm long. Rhachis (female) fragile at the nodes; subcylindrical and excavated; 2–3 mm wide. Spikelet packing abaxial. Rhachis internodes oblong; 2–3 mm long; adherent to upper glume of sessile spikelet. Rhachis internode tip transverse; crateriform.

Sexes segregated; on bisexual branches; with male above. Spikelets sunken; solitary. Fertile spikelets sessile. Male spikelets sessile and pedicelled; 2 in a cluster. Pedicels (male) 2.5–7 mm long.

FERTILE SPIKELETS Spikelets comprising 1 basal sterile florets; 1 fertile florets; without rhachilla extension. Spikelets ovate; dorsally compressed; 5 mm long; falling entire; deciduous with accessory branch structures. Spikelet callus base truncate; with central peg; attached transversely.

GLUMES Glumes dissimilar; reaching apex of florets; firmer than fertile lemma; shiny. Lower glume ovate; 1 length of spikelet; indurate; without keels. Lower glume apex acute. Upper glume ovate; cartilaginous; without keels. Upper glume apex acute.

FLORETS Basal sterile florets barren; without significant palea. Lemma of lower sterile floret oblong; hyaline. Fertile florets female. Fertile lemma oblong; hyaline; without keel. Palea hyaline.

MALE Male spikelets distinct from female; with free pedicels; all deciduous together; 4–6 mm long. Male spikelet glumes 2; membranous; muticous.

DISTRIBUTION North America: Mexico. South America: Mesoamericana.

NOTES Andropogoneae. Fl Meso-Am 1995.

ADDITIONAL CHARACTERS Male internodes 0.3–0.5mm wide.

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