17.04   DISTICHLIS Raf.

Mary E. Barkworth

Hester L. Bell

Plants perennial; usually unisexual, occasionally bisexual; strongly rhizomatous and/or stoloniferous. Culms to 60 cm, usually erect, glabrous. Leaves conspicuously distichous; lower leaves reduced to scalelike sheaths; upper leaf sheaths strongly overlapping; ligules shorter than 1 mm, membranous, serrate; upper blades stiff, glabrous, ascending to spreading, usually equaling or exceeding the pistillate panicles. Inflorescences terminal, contracted panicles or racemes, sometimes exceeding the upper leaves. Spikelets laterally compressed, with 2-20 florets; disarticulation of the pistillate spikelets above the glumes and below the florets, staminate spikelets not disarticulating. Glumes 3-7-veined; lemmas coriaceous, staminate lemmas thinner than the pistillate lemmas, 9-11-veined, unawned; paleas 2-keeled, keels narrowly to broadly winged, serrate to toothed, sometimes with excurrent veins; anthers 3. Caryopses glabrous, free from the palea at maturity, brown. x = 10. Name from the Greek distichos, two-rowed, referring to the conspicuously distichous blades.

Distichlis, a genus of about sever species, grows in saline soils of the coasts and interior deserts of the Western Hemisphere and Australia. All the species grow in South America, two grow in North America. This treatment has been revised in accordance with the recommendations in Bell and Columbus (2008).

SELECTED REFERENCES Beetle, A.A. 1943. The North American variations of Distichlis spicata. Bull. Torrey Bot. Club 70:638-650; Bell, H.L. and J.T. Columbus. 2008. Proposal for an expanded Distichlis (Poaceae, Chloridoideae): support from molecular, morphological, and anatomical characters. Systematic Botany 33(3): 536-55; Harrington, J., S. Reid, W. Black, and M. Brick. 2009. Was Rydberg Right? Evidence for Distichlis stricta as a species distinct from D. spicata. Abstract for Botany 2009; López Soto, M.M, S.D. Koch, M. Flores-Cruz, and E. M. Engleman. 2009. Anatomía comparada de la lamina foliar del género Distichlis (Poaceae). Acta Botanica Mexicana 89:1-23. Villamil, C.B. 1969. El género Monanthochloë (Gramineae). Estudios morfológicos y taxonómicos con especial referencia a la especie Argentina. Kurtziana 5:369-391.


1. Inflorescences with multiple spikelets; leaf blades 1-8(20) cm, stiff or lax ..... D. spicata

1. Inflorescences composed of a single spikelet; leaf blades 0.5-1.5 cm long, stiff ..... D. littoralis

1.   Distichlis spicata (L.) Greene

Plants rhizomatous and sometimes stoloniferous. Culms 10-60 cm, usually erect, sometimes decumbent or prostrate. Blades of upper leaves 1-8(20) cm, rigid and divaricate to lax and ascending, usually equaling or exceeding the pistillate panicles, varying with respect to the staminate panicles. Pistillate panicles 1-7 cm, often congested, with 2-20 spikelets. Pistillate spikelets 5-20 mm long, 4-7 mm wide, with 5-20 florets; lower glumes 2-3 mm; upper glumes 3-4 mm; lemmas 3.5-6 mm; paleas with serrate keels. Caryopses 2-5 mm, tapered or truncate. Staminate panicles and spikelets similar to the pistillate panicles and spikelets, but the lemmas somewhat thinner in texture and the paleas not bowed-out. Anthers 3-4 mm. 2n = 40.

Distichlis spicata grows in saline soils of the Western Hemisphere and Australia. Numerous infraspecific taxa have been recognized in the past, but none appears to be justified. Recent North American accounts of Distichlis have usually recognized plants from maritime coasts as distinct from those growing inland, supposedly having more congested inflorescences, but the range of variation is similar in the two habitats.

López Soto et al. (2009) examined the leaf anatomy of six species and 11 varieties of Distichlis. They found that D. australis and D. palmeri differed from all other species and that D. humilis, D. spicata, and D. scoparia were anatomically similar but distinguishable. They found no characters or character combinations that supported recognition of infraspecific taxa within D. spicata. Harrington et al. (2009), on the other hand, found that inland plants, which Rydberg called D. stricta, differed from coastal plants in molecularly, cytogenetically, and in their phenology. On that basis, it seems that treatment of the inland plants as D. spicata subsp. stricta (Torr.) Thorne is warranted. The reason for no treating them as species is pragmatic, the lack of morphological characters for distinguishing them.

2.   Distichlis littoralis (Engelm.) H.L. Bell and Columbus

Plants with long, wiry stolons. Culms 8-15 cm, clustered, erect, with numerous short, leafy, lateral branches. Leaves clustered on distant to closely-spaced, short, lateral shoots; sheaths 4-6 mm, rounded, smooth, shiny, glabrous or puberulent at the base; ligules thickly membranous ciliate rims; blades 0.5-1.5 cm long, 1-2(3) mm wide, stiff, subulate, uniformly many-veined. Inflorescences terminal, composed of a single glabrous spikelet, this enclosed, and almost concealed, by the uppermost leaf sheaths. Pistillate spikelets subterete, with 3-5 florets, distal florets rudimentary; disarticulation tardy, below the lowest floret; glumes absent; lemmas coriaceous, glabrous, 9-veined, acute; paleas coriaceous, keels prominently winged, wings overlapping and enclosing the caryopses. Staminate spikelets similar to the pistillate spikelets, but smaller and the glumes and lemmas thinner. x = 10. Name from the Greek monos, single, anthos, flower, and chloë, grass, alluding to the solitary spikelets. 2n = 40.

Distichlis littoralis grows in moist, sandy, saline soils along the coast of southern California and the southeastern United States, northeastern Mexico, and the Caribbean islands. It was previously placed in Monanthochlo
ë but Bell and Columbus (2008) demonstrated that Monanthochloë is nested within Distichlis.