The grass genera of the world
~ Distichlis (D. texana)
Habit, vegetative morphology. Perennial; rhizomatous and stoloniferous (the stolons long and stout). Culms 70–100 cm high; herbaceous. Culm nodes glabrous. Plants unarmed. Leaves not basally aggregated; non-auriculate. Leaf blades linear; narrow; 3–5 mm wide (to 30 cm long); flat; without abaxial multicellular glands; without cross venation; persistent. Ligule a fringe of hairs (very dense). Contra-ligule absent.
Reproductive organization. Plants dioecious; without hermaphrodite florets. The spikelets all alike in sexuality (on the same plant); female-only, or male-only. Plants outbreeding.
Inflorescence. Inflorescence paniculate (in both female and male plants); open; non-digitate; espatheate; not comprising partial inflorescences and foliar organs. Spikelet-bearing axes persistent. Spikelets solitary; not secund; pedicellate.
Female-sterile spikelets. Male spikelets 10–15 mm long, with up to 20 florets; florets with three stamens. Rachilla of male spikelets prolonged beyond the uppermost male floret. The male spikelets with glumes; 10–20 floreted. Male florets 3 staminate.
Female-fertile spikelets. Spikelets 9–15 mm long; compressed laterally; disarticulating above the glumes; disarticulating between the florets; with conventional internode spacings (though these longish). Rachilla prolonged beyond the uppermost female-fertile floret; hairless; the rachilla extension with incomplete florets. Hairy callus absent. Callus glabrous, spongy, somewhat distended.
Glumes two; relatively large; more or less equal; shorter than the spikelets; shorter than the adjacent lemmas; hairless (minutely scabrid on the keel); pointed; awnless; carinate; similar (broadly lanceolate, membranous). Lower glume 3 nerved. Upper glume 5 nerved. Spikelets with incomplete florets. The incomplete florets distal to the female-fertile florets. The distal incomplete florets merely underdeveloped.
Female-fertile florets 4–6. Lemmas similar in texture to the glumes (membranous, the very wide hyaline margins enveloping the florets above); smooth; not becoming indurated; entire; pointed; awnless; hairless; glabrous; slightly carinate; without a germination flap; 3–4 nerved. Palea present; relatively long; convolute around the flower (saccate below, closely convolute around the pistil); entire; awnless, without apical setae (but often delicately ciliate); textured like the lemma; not indurated; 2-nerved; 2-keeled. Palea keels winged (with conspicuous, hyaline wings); hairy (ciliate). Lodicules present; 2; free; fleshy to membranous (not cuneate, but apically thicker than the usual membranous type); ciliate; lobed; heavily vascularized. Stamens 0 (represented by three minute, flattened, lodicule-like staminodes). Ovary apically glabrous. Styles fused (ovary attenuate into a long style). Stigmas 2 (exserted).
Fruit, embryo and seedling. Fruit ellipsoid.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; more or less spherical to elongated; clearly two-celled; chloridoid-type (but apical cells thin-walled). Microhair apical cell wall thinner than that of the basal cell but not tending to collapse. Microhairs 27–31.5 microns long. Microhair basal cells 18–21 microns long. Microhairs 12–13.5 microns wide at the septum. Microhair total length/width at septum 2.2–2.6. Microhair apical cells 12–13.5 microns long. Microhair apical cell/total length ratio 0.4–0.44. Stomata common; 27–31.5 microns long. Subsidiaries mostly low to medium dome-shaped. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs, or not paired; silicified. Intercostal silica bodies present and perfectly developed; crescentic, or tall-and-narrow. Costal short-cells conspicuously in long rows. Costal silica bodies present in alternate cell files of the costal zones; panicoid-type; predominantly shortly cross shaped, dumb-bell shaped, and nodular.
Transverse section of leaf blade, physiology. Lamina mid-zone in transverse section open.
C4; XyMS+. PCR sheaths of the primary vascular bundles complete. PCR sheath extensions absent. Mesophyll traversed by columns of colourless mesophyll cells. Leaf blade nodular in section; with the ribs more or less constant in size. Midrib not readily distinguishable; with one bundle only. Bulliforms present in discrete, regular adaxial groups; associated with colourless mesophyll cells to form deeply-penetrating fans. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present; forming figures (with most bundles). Sclerenchyma all associated with vascular bundles. The lamina margins with fibres.
Cytology. Chromosome base number, x = 10. 2n = 40. 4 ploid.
Classification. Watson & Dallwitz (1994): Chloridoideae; main chloridoid assemblage. Soreng et al. (2015): Chloridoideae; Cynodonteae. 1 species (A. verticillatum).
Distribution, phytogeography, ecology. Southern United States.
Species of open habitats; seemingly glycophytic (by contrast with the related Distichlis). Sandy places.
References, etc. Morphological/taxonomic: Soderstrom and Decker 1965. Leaf anatomical: studied by us.
Special comments. Fruit data wanting. Illustrations. • A. texana (as Distichlis): Hitchcock and Chase (1950)
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. delta-intkey.com/grass’.