Neil Snow

Plants annual or perennial; cespitose. Culms (3)10-250(300) cm, usually ascending to erect, often geniculate at the lower nodes, occasionally prostrate and rooting at the lower nodes, often branching at the aerial nodes; nodes usually glabrous; internodes usually hollow. Leaves usually primarily cauline, occasionally in basal rosettes; sheaths open; ligules 0.2-10(15) mm, obtuse to attenuate, usually membranous, sometimes ciliate; blades flat, involute when dry, usually ascending to erect, apices attenuate. Primary inflorescences terminal, panicles of 2-150 non-disarticulating, spikelike branches, usually exceeding the leaves; branches 1-22 cm, digitate, subdigitate, or racemose on the rachises, 1-sided, usually spikelet-bearing throughout their length, spikelets in 2 rows, axes terminating in a functional spikelet, lower branches occasionally with secondary branching; secondary panicles sometimes present, axillary to and concealed by the lower sheaths, their florets not disarticulating; disarticulation in the primary panicles beneath the florets. Spikelets rounded to slightly keeled on the back, distant to tightly imbricate, not conspicuously pubescent, with (2)3-12(20) bisexual florets; rachillas rarely prolonged. Glumes usually unequal, sometimes subequal, exceeded by the florets, membranous, rounded to weakly keeled, 1-veined, veins scabrous, apices unawned (rarely mucronate); lower glumes 0.5-4.9 mm; upper glumes 0.9-6 mm; florets usually bisexual; callusesdistinct or poorly developed, glabrous or pubescent; lemmas membranous, usually pubescent at least over the lower portion of the veins, 3(5)-veined, apices entire or minutely bilobed, unawned, mucronate, or awned; paleas usually subequal to the lemmas, membranous or hyaline; anthers 1-3, 0.1-2.7 mm. Caryopses obovate to elliptic, falling free of the lemmas and paleas. x = 10. Name from the Greek leptos, slender, in reference to the panicle branches, and chloa, grass.

Leptochloa is a pantropical, warm-temperate genus of 32 species. Eight of the ten species in this treatment are native to the Flora region. Of the other two, L. chloridiformis was introduced over 60 years ago but has not become established. Leptochloa chinensis is not yet known from the region; it is included here because of its potential threat as an invasive weed. Cladistic studies (Snow 1997) do not support recognition of the segregate genus Diplachne.

Leptochloa tends to grow in somewhat basic soils. Many of the species, particularly the annual species, are poor ecological competitors and grow in relatively open, seasonally inundated soils, such as are found along rivers. In disturbed areas, they are associated with roadside ditches, the margins of reservoirs, and mesic agricultural lands. A few species, primarily perennial, grow on well-drained soils. The vegetative vigor of all species is greatly influenced by soil moisture availability.

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SELECTED REFERENCES Nicora, E.G. 1995. Los géneros Diplachne y Leptochloa (Gramineae, Eragrosteae) de la Argentina y países limítrofes. Darwiniana 33:233-256; Snow, N. 1997. Phylogeny and systematics of Leptochloa P. Beauv. sensu lato (Poaceae, Chloridoideae). Ph.D. dissertation, Washington University, St. Louis, Missouri, U.S.A. 506 pp.; Snow, N. 1998. Nomenclatural changes in Leptochloa P. Beauvois sensu lato (Poaceae, Chloridoideae). Novon 8:77-80.

Peterson, P.M., K. Romaschenko, N. Snow, & G. Johnson (2012) A molecular phylogeny of Leptochloa (Poaceae: Chloridoideae: Chlorideae). Ann. Bot. 109: 1317–1329. 

Snow, N. & P.M. Peterson (2012) Nomenclatural notes on Dinebra, Diplachne, Disakisperma, and Leptochloa (Poaceae: Chlorioideae). Phytoneuron 2012-71:1-2. ISSN 2153 733X.

Snow, N., P.M. Peterson, K. Romaschenko (2013) Systematics of Disakisperma (Poaceae, Chloridoideae, Chlorideae). PhytoKeys 26: 21–70. doi: 10.3897/phytokeys.26.5649

Snow, N., P.M. Peterson, K. Romaschenko, B.K. Simon (2018) Monograph of Diplachne (Poaceae, Chloridoideae, Cynodonteae). PhytoKeys 93: 1-102. https://doi.org/10.3897/phytokeys.93.21079