The grass genera of the world
Habit, vegetative morphology. Annual; culms ascending or decumbent, not producing juvenile floating leaves. Culms herbaceous. Culm internodes solid. The shoots aromatic. Leaves not basally aggregated; not clearly differentiated into sheath and blade; distichous; non-auriculate. Leaf blades narrow; 5–12 mm wide; flat, or rolled; exhibiting multicellular glands abaxially. The abaxial leaf blade glands intercostal. Leaf blades without cross venation; persistent. Ligule absent.
Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets.
Inflorescence. Inflorescence dense, many sided, a single spike, or a single raceme; espatheate; not comprising partial inflorescences and foliar organs. Spikelet-bearing axes persistent. Spikelets not secund; not two-ranked (spiralled); sessile to subsessile.
Female-fertile spikelets. Spikelets compressed laterally; disarticulating above the glumes; disarticulating between the florets. Rachilla prolonged beyond the uppermost female-fertile floret; the rachilla extension with incomplete florets.
Glumes two; more or less equal; shorter than the adjacent lemmas; not pointed; awnless; similar (broad, 2–5 toothed). Lower glume 9–15 nerved. Upper glume 9–15 nerved. Spikelets with incomplete florets. The incomplete florets distal to the female-fertile florets.
Female-fertile florets 5–30(–40). Lemmas entire, or incised; not deeply cleft (entire, erose or denticulate); awnless, or mucronate (usually, centrally); 11–17 nerved. Palea present; relatively long; 2-nerved; 2-keeled. Palea keels wingless; glabrous. Lodicules present (minute, often fused to the palea); 2; fleshy. Stamens 3. Ovary apically glabrous. Stigmas 2.
Fruit, embryo and seedling. Fruit not viscid; compressed laterally. Hilum short. Pericarp fused. Embryo large (clearly visible through the pericarp); 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 absent. Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; more or less spherical to elongated; ostensibly one-celled to clearly two-celled; chloridoid-type (of the sunken, button mushroom type); (10.5–)12–15(–18) microns long; 9–12–13.5 microns wide at the septum. Microhair total length/width at septum 1–1.3. Microhair apical cells (6–)6.6–7.5(–10.5) microns long. Microhair apical cell/total length ratio 0.47–0.63. Stomata common; (21–)24–27(–29) microns long. Subsidiaries parallel-sided (broadly), or dome-shaped. Guard-cells overlapped by the interstomatals. Intercostal short-cells absent or very rare. Intercostal silica bodies absent. With costal prickles and long, thin intercostal macrohairs. Costal zones with short-cells. Costal short-cells conspicuously in long rows. Costal silica bodies present in alternate cell files of the costal zones; panicoid-type; nodular (mostly, elongated), or dumb-bell shaped; not sharp-pointed.
Transverse section of leaf blade, physiology. Lamina mid-zone in transverse section open.
C4; XyMS+. PCR sheath extensions absent. Midrib seemingly not readily distinguishable; with one bundle only. Bulliforms present in discrete, regular adaxial groups (in the furrows, the details not observable in material seen). All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present (only some of the major bundles). Sclerenchyma all associated with vascular bundles.
Cytology. Chromosome base number, x = 10. 2n = 24 and 40. 2 and 4 ploid (and aneuploids).
Classification. Watson & Dallwitz (1994): Chloridoideae; Orcuttieae. Soreng et al. (2015): Chloridoideae; Cynodonteae; Orcuttiinae. 3 species.
Distribution, phytogeography, ecology. California and Mexico.
References, etc. Morphological/taxonomic: Reeder 1965. Leaf anatomical: studied by us - T. greenei (Vasey) J. Reeder.
Illustrations. • T. greenei, as Orcuttia: Vasey, Ill. N. Amer. Grasses (1893). • T. fragilis, as Orcuttia: Gleason et al., Phytologia (1980)
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’.