The grass genera of the world
~ Rytidosperma, Danthonia sensu lato
Habit, vegetative morphology. Low, mat-forming perennial; rhizomatous and caespitose. Culms 1–3 cm high; herbaceous. Culm nodes glabrous. Culm internodes solid. Leaves mostly basal; non-auriculate. Leaf blades narrow; setaceous to not setaceous; folded; without cross venation; persistent.
Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets.
Inflorescence. Inflorescence reduced to a single spikelet, or few spikeleted (1–3); a single raceme, or paniculate (much reduced); espatheate; not comprising partial inflorescences and foliar organs. Spikelet-bearing axes persistent.
Female-fertile spikelets. Spikelets compressed laterally; disarticulating above the glumes; disarticulating between the florets. Rachilla prolonged beyond the uppermost female-fertile floret; hairy, or hairless. Hairy callus absent. Callus very short.
Glumes present; two; more or less equal; exceeding the spikelets (enclosing it); long relative to the adjacent lemmas; hairless; glabrous; awnless; similar (ovate, leathery). Lower glume 7–9 nerved. Upper glume 7–9 nerved. Spikelets with female-fertile florets only, or with incomplete florets. The incomplete florets distal to the female-fertile florets. The distal incomplete florets merely underdeveloped.
Female-fertile florets 2–3. Lemmas similar in texture to the glumes (leathery); not becoming indurated; incised; minutely 3 lobed (3-toothed); not deeply cleft; mucronate (on the teeth); hairy (minutely pilose). The hairs not in tufts; not in transverse rows. Lemmas non-carinate; 9 nerved. Palea present; 2-nerved. Lodicules present; 2; free; fleshy; ciliate. Stamens 3. Anthers not penicillate. Ovary apically glabrous. Styles free to their bases. Stigmas 2.
Fruit, embryo and seedling. Fruit small; compressed dorsiventrally. Hilum short. Pericarp thick and hard; free (the fruit a tiny nut). Embryo large; waisted; without an epiblast; with a scutellar tail.
Ovule, embryology. Outer integument covering no more than the chalazal half of the ovule. Inner integument discontinuous distally. Synergids haustorial.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells similar in shape costally and intercostally; of similar wall thickness costally and intercostally. Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; panicoid-type to chloridoid-type; (45–)51–63(–66) microns long; (22.5–)24–25.5(–26.4) microns wide at the septum. Microhair total length/width at septum 1.8–2.6. Microhair apical cells (13.5–)18–24(–25.5) microns long. Microhair apical cell/total length ratio 0.3–0.45. Stomata common; (39–)40–47(–48) microns long. Subsidiaries dome-shaped, or triangular. Guard-cells overlapped by the interstomatals, or overlapping to flush with the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs; silicified. Costal short-cells conspicuously in long rows, or neither distinctly grouped into long rows nor predominantly paired. Costal silica bodies rounded, crescentic, and panicoid-type; often cross shaped; not sharp-pointed.
Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll with non-radiate chlorenchyma; without adaxial palisade. Leaf blade adaxially flat. Midrib conspicuous; with one bundle only. Bulliforms not present in discrete, regular adaxial groups (confined to a simple fan over the midrib). Many of the smallest vascular bundles unaccompanied by sclerenchyma. Combined sclerenchyma girders present; forming figures. Sclerenchyma all associated with vascular bundles.
Classification. Watson & Dallwitz (1994): Arundinoideae; Danthonieae. Soreng et al. (2015): Danthonioideae; Danthonieae. 1 species (P. exigua).
Distribution, phytogeography, ecology. New Zealand.
Species of open habitats; glycophytic. Upland grassy plains.
References, etc. Morphological/taxonomic: Zotov 1963. Leaf anatomical: studied by us.
Illustrations. • P. exigua, abaxial epidermis of leaf blade: this project. • P. exigua, abaxial epidermis of leaf blade: this project
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’.