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The grass genera of the world

L. Watson, T.D. Macfarlane, and M.J. Dallwitz

Distichlis Raf.

From the Greek distichos (in 2 rows), referring to the conspicuous phyllotaxy.

Type species: Type: D. maritima Raf., nom. illeg..

Including Trisiola Raf. (1825)

Excluding Allolepis (D. texana), Monanthochloë, Reederochloa

Habit, vegetative morphology. Perennial; saltgrass, with thick, conspicuously distichous leaves. Culms 10–70 cm high; herbaceous. Culm nodes glabrous. Culm internodes solid. Leaves not basally aggregated; non-auriculate. Leaf blades narrow; without abaxial multicellular glands; without cross venation; disarticulating from the sheaths; rolled in bud. Ligule a fringed membrane to a fringe of hairs (?).

Reproductive organization. Plants monoecious with all the fertile spikelets unisexual (rarely), or dioecious; without hermaphrodite florets. The spikelets of sexually distinct forms on the same plant (when monoecious), or all alike in sexuality (on the same plant, i.e., when dioecious); female-only, or male-only, or female-only and male-only. Plants outbreeding (at least when dioecious).

Inflorescence. Inflorescence reduced to a single spikelet (D. australis), or few spikeleted, or many spikeleted; of spicate main branches (of short racemes on a central axis), or a single raceme, or paniculate (or reduced); contracted; more or less ovoid, or spicate, or more or less irregular; non-digitate; espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets solitary; not secund; pedicellate.

Female-sterile spikelets. Male spikelets similar to the females, but of thinner texture. Male florets 3 staminate.

Female-fertile spikelets. Spikelets 6–28 mm long; compressed laterally; tardily disarticulating above the glumes; disarticulating between the florets. Rachilla prolonged beyond the uppermost female-fertile floret; hairless. Hairy callus absent.

Glumes two; very unequal; shorter than the spikelets; shorter than the adjacent lemmas; pointed; awnless; similar (firm). Lower glume 1–5 nerved. Upper glume 4–9 nerved. Spikelets without proximal incomplete florets.

Female-fertile florets 3–20. Lemmas not becoming indurated; entire; pointed; awnless; hairless; glabrous; carinate to non-carinate; (3–)7–9(–11) nerved. Palea present; relatively long; not convolute; leathery; 2-nerved; 2-keeled. Palea keels more or less winged. Lodicules present; 2; free; fleshy, or membranous; glabrous; toothed. Stamens 0. Ovary apically glabrous. Styles free to their bases. Stigmas 2.

Fruit, embryo and seedling. Fruit ellipsoid. Hilum short. Endosperm hard; containing only simple starch grains. Embryo with an epiblast; with a scutellar tail; with an elongated mesocotyl internode. Embryonic leaf margins meeting.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae present (a few, usually near stomata), or absent (but abundant adaxially); intercostal. Intercostal papillae over-arching the stomata to not over-arching the stomata; consisting of one oblique swelling per cell. Long-cells similar in shape costally and intercostally; of similar wall thickness costally and intercostally (fairly thick walled). Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present, or absent; more or less spherical, or elongated; ostensibly one-celled, or clearly two-celled; chloridoid-type. Microhair apical cell wall of similar thickness/rigidity to that of the basal cell. Microhairs with ‘partitioning membranes’ (in D. stricta). The ‘partitioning membranes’ in the basal cell. Microhairs when seen 30–32 microns long. Microhair basal cells 24 microns long. Microhairs about 13 microns wide at the septum. Microhair total length/width at septum 2.3. Microhair apical cells 7.5 microns long. Microhair apical cell/total length ratio 0.24. Stomata common; 21–24 microns long. Subsidiaries dome-shaped, or dome-shaped and triangular. Guard-cells overlapped by the interstomatals, or overlapping to flush with the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs (occasionally), or not paired (solitary); silicified (rarely), or not silicified. Intercostal silica bodies absent, or imperfectly developed; when present, tall-and-narrow. Costal short-cells predominantly paired, or neither distinctly grouped into long rows nor predominantly paired. Costal silica bodies present throughout the costal zones; rounded (common), or saddle shaped, or tall-and-narrow (or more or less cuboid).

Transverse section of leaf blade, physiology. Lamina mid-zone in transverse section open.

C4; XyMS+. PCR sheath outlines even. PCR sheaths of the primary vascular bundles interrupted; interrupted abaxially only. PCR sheath extensions present. Maximum number of extension cells 1. PCR cell chloroplasts centripetal. Mesophyll with radiate chlorenchyma; traversed by columns of colourless mesophyll cells. Leaf blade with distinct, prominent adaxial ribs; with the ribs more or less constant in size. Midrib not readily distinguishable; with one bundle only. Bulliforms present in discrete, regular adaxial groups; in simple fans (irregular, of small cells), or associated with colourless mesophyll cells to form deeply-penetrating fans (sometimes connected with traversing colourless columns). All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present; forming ‘figures’. Sclerenchyma all associated with vascular bundles. The lamina margins with fibres.

Phytochemistry. Tissues of the culm bases with abundant starch. Leaves without flavonoid sulphates (1 species).

Cytology. Chromosome base number, x = 10. 2n = 40 (in D. stricta). 4 ploid.

Classification. Watson & Dallwitz (1994): Chloridoideae; main chloridoid assemblage. Soreng et al. (2015): Chloridoideae; Cynodonteae; Monanthochloinae. About 6 species.

Distribution, phytogeography, ecology. America and Australia.

Species of open habitats; halophytic. Seashores and deserts.

Economic aspects. Significant weed species: D. spicata, D. stricta.

Rusts and smuts. Rusts — Puccinia. Smuts from Ustilaginaceae. Ustilaginaceae — Ustilago.

References, etc. Leaf anatomical: Metcalfe 1960; studied by us - D. distichophylla (Labill.) Fassett.

Special comments. Fruit data wanting. Illustrations. • D. spicata, male (as Poa thalassica): Kunth (1835). • D. spicata, female (as Poa thalassica): Kunth (1835). • D. distochophylla, spikelets: this project. • D. distichophylla, abaxial epidermis of leaf blade: this project. • D. distichophylla, abaxial epidermis of leaf blade: this project. • Pollen antigens: Watson and Knox (1976)

We advise against extracting comparative information from the descriptions. This is much more easily achieved using the DELTA data files or the interactive key, which allows access to the character list, illustrations, full and partial descriptions, diagnostic descriptions, differences and similarities between taxa, lists of taxa exhibiting or lacking specified attributes, distributions of character states within any set of taxa, geographical distribution, and classifications. See also Guidelines for using data taken from Web publications.

Cite this publication as: ‘Watson, L., Macfarlane, T.D., and Dallwitz, M.J. 1992 onwards. The grass genera of the world: descriptions, illustrations, identification, and information retrieval; including synonyms, morphology, anatomy, physiology, phytochemistry, cytology, classification, pathogens, world and local distribution, and references. Version: 11th December 2017.’.