The grass genera of the world
~ Erioneuron (E. pulchellum), Tridens (T. pulchellus)
Habit, vegetative morphology. Mop-like perennial; caespitose, or stoloniferous and caespitose. Culms 5–15 cm high; herbaceous; branched above. Leaves not basally aggregated. Leaf blades narrow; 0.3–0.5 mm wide; setaceous; rolled (involute); without abaxial multicellular glands; not pseudopetiolate; without cross venation. Ligule present; a fringe of hairs.
Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets.
Inflorescence. Inflorescence few spikeleted; paniculate; contracted (short peduncled, consisting of 3-spikeleted racemes); non-digitate; spatheate (each raceme subtended by a subulate-tipped sheath); a complex of partial inflorescences and intervening foliar organs. Spikelet-bearing axes persistent.
Female-fertile spikelets. Spikelets 4–6 mm long; compressed laterally (plump); disarticulating above the glumes; disarticulating between the florets; with conventional internode spacings. Rachilla prolonged beyond the uppermost female-fertile floret; the rachilla extension naked.
Glumes two; very unequal to more or less equal; about equalling the spikelets; (the longer) long relative to the adjacent lemmas; hairless; pointed; shortly awned (to mucronate); carinate; similar (membranous, with glands at the base). Lower glume 1 nerved. Upper glume 1 nerved. Spikelets with female-fertile florets only.
Female-fertile florets 2. Lemmas similar in texture to the glumes (thinly membranous); not becoming indurated; incised; 2 lobed; deeply cleft (to about halfway); awned. Awns 1; median; from a sinus; non-geniculate; hairless; much shorter than the body of the lemma to about as long as the body of the lemma; entered by one vein. Lemmas hairy; non-carinate; without a germination flap; 3 nerved (the laterals sub-marginal). Palea present; relatively long; entire; awnless, without apical setae (hairy below and on the keels); not indurated; 2-nerved; 2-keeled. Stamens 3 (?). Ovary apically glabrous. Stigmas 2; white.
Fruit, embryo and seedling. Fruit ellipsoid; compressed laterally. Hilum short. Pericarp fused. Embryo large; with an epiblast; with a scutellar tail; with an elongated mesocotyl internode. Embryonic leaf margins meeting.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous (the intercostal zones in furrows, and obscured by long prickles). Papillae absent. Long-cells markedly different in shape costally and intercostally (the costals much more regularly rectangular); of similar wall thickness costally and intercostally. Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs absent (none seen - but they would be hard to find in such material). Stomata common (hidden in the sides of the furrows, except towards the blade margins); 24–30 microns long. Subsidiaries low to high dome-shaped (mostly), or triangular (a few). Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells absent or very rare; not paired. Intercostal silica bodies absent. Simple, thick walled prickles abundant costally and intercostally. Crown cells absent. Costal short-cells predominantly paired. Costal silica bodies present throughout the costal zones; panicoid-type, or crescentic (a few, plump), or rounded (a few, merging with crosses and crescents); basically cross shaped (often more or less malformed to simulate the other forms).
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 complete. PCR sheath extensions absent. PCR cell chloroplasts centripetal. Mesophyll with radiate chlorenchyma; traversed by columns of colourless mesophyll cells. Leaf blade nodular in section to adaxially flat; with the ribs more or less constant in size (round topped). Midrib conspicuous to not readily distinguishable (having a somewhat larger abaxial strand); with one bundle only. The lamina symmetrical on either side of the midrib. Bulliforms present in discrete, regular adaxial groups; associated with colourless mesophyll cells to form deeply-penetrating fans (these incorporated in the traversing colourless columns). All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders absent (all the bundles with large adaxial and massive abaxial strands only). Sclerenchyma all associated with vascular bundles (except for large marginal groups). The lamina margins with fibres (large).
Cytology. Chromosome base number, x = 8. 2n = 16. 2 ploid.
Classification. Watson & Dallwitz (1994): Chloridoideae; main chloridoid assemblage. Soreng et al. (2015): Chloridoideae; Cynodonteae; Scleropogoninae. 1 species (D. pulchella).
Distribution, phytogeography, ecology. Southern U.S.A. and Mexico.
Xerophytic; species of open habitats. Rocky slopes.
References, etc. Morphological/taxonomic: Sanchez 1983. Leaf anatomical: studied by us.
Illustrations. • D. pulchella, as Tridens: Hitchcock & 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’.