The grass genera of the world
Including Arthrochlaena Laena
Habit, vegetative morphology. Perennial; stoloniferous and caespitose. Culms 30–80 cm high (rigid); unbranched above. Culm nodes glabrous. Culm internodes solid. Plants conspicuously armed (the rigid leaves sharp-pointed). Leaves mostly basal; non-auriculate. Leaf blades acicular (junciform, circular in section, longitudinally striate, with a central pith); hard, woody, needle-like; without abaxial multicellular glands. Ligule a fringe of hairs (short, dense). Contra-ligule absent.
Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets. The spikelets all alike in sexuality (except for reduced members at the tips of the spikes).
Inflorescence. Inflorescence of spicate main branches; digitate. Primary inflorescence branches 2–4. Inflorescence with axes ending in spikelets (but these more or less abortive), or axes not ending in spikelets (ending in a point). Inflorescence espatheate; not comprising partial inflorescences and foliar organs. Spikelet-bearing axes spikes (3–15 cm long); persistent. Spikelets solitary; secund; biseriate; sessile; imbricate.
Female-fertile spikelets. Spikelets 10–21 mm long (by 4–5 mm wide); strongly compressed laterally; disarticulating above the glumes; disarticulating between the florets; with conventional internode spacings. Rachilla prolonged beyond the uppermost female-fertile floret; hairless (glabrous); the rachilla extension with incomplete florets. Hairy callus absent.
Glumes two; very unequal (G1 about half the length of G2); shorter than the spikelets; shorter than the adjacent lemmas (G2 reaching about the middle of L1); lateral to the rachis (i.e. the spikelet edgewise to the rachis); hairless; glabrous; pointed (acute); awnless; carinate; similar (ovate-acute, leathery, the upper sometimes pungent tipped). Lower glume 1 nerved. Upper glume 1 nerved. Spikelets with incomplete florets. The incomplete florets distal to the female-fertile florets. The distal incomplete florets merely underdeveloped. Spikelets without proximal incomplete florets.
Female-fertile florets 6–20. Lemmas similar in texture to the glumes (leathery); smooth; not becoming indurated; entire to incised; not deeply cleft (no more than minutely incised); awnless (but mucronulate), or mucronate (minutely, from the median nerve); hairless; glabrous; strongly carinate; without a germination flap; 3 nerved. Palea present; relatively long; minutely apically notched; awnless, without apical setae (glabrous); not indurated (but almost cartilaginous); 2-nerved; 2-keeled. Palea keels winged; minutely ciliolate. Lodicules present; 2; free; membranous; glabrous; toothed; very heavily vascularized (at the base). Stamens 3; with free filaments (these long). Ovary apically glabrous. Styles free to their bases (the bases swollen). Stigmas 2.
Fruit, embryo and seedling. Fruit small; ellipsoid; not noticeably compressed. Hilum short. Pericarp free (very flimsy). Embryo large; waisted.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae present; intercostal. Intercostal papillae over-arching the stomata; consisting of one symmetrical projection per cell (the intercostal grooves filled with short, blunt, thick-walled, unicellular papilla-hairs). Intercostal zones details of intercostal zones invisible. Microhairs present (Chloris type, hard to find among the papilla-hairs in the leaf grooves); more or less spherical; ostensibly one-celled; chloridoid-type; (33–)39–42(–45) microns long. Microhair total length/width at septum 1.6–2. Stomata common (in the grooves); (16.5–)18–21(–27) microns long. Subsidiaries triangular. Costal short-cells neither distinctly grouped into long rows nor predominantly paired. Costal silica bodies present throughout the costal zones; rounded and saddle shaped (intergrading); not sharp-pointed.
Transverse section of leaf blade, physiology. Lamina mid-zone in transverse section terete.
C4 (vascular bundles in a single ring at the periphery of the pith, linked with the epidermis by tall columns of sclerenchyma; rows of PCR cells adjacent to the sclerenchyma blocks, not sheathing the bundles (sometimes the PCR rows link internally between the bundles; cf. Triodia); blocks of PCA tissue sandwiched and enclosed between the PCR cell rows). The anatomical organization unconventional. Organization of PCR tissue Triodia type. XyMS+. Mesophyll with arm cells (abundant, very clear). All the vascular bundles accompanied by sclerenchyma (all bundles with elongated, outer girders). Sclerenchyma not all bundle-associated. The extra sclerenchyma in adaxial groups (morphologically so, being internal to the ring of bundles).
Classification. Watson & Dallwitz (1994): Chloridoideae; main chloridoid assemblage. Soreng et al. (2015): Chloridoideae; Cynodonteae; Eleusininae. 1 species.
Distribution, phytogeography, ecology. Madagascar, Aldabra, Assumption.
Xerophytic (extreme); species of open habitats; halophytic (coral rocks, salt pans, mangrove swamps).
References, etc. Leaf anatomical: this project.
Special comments. Rows of crypts containing crystalline material (NaCl?) occur within the grooves if the leaf blade. Illustrations. • S. macrostachyum, as S. juncifolium: Hook. Ic. Pl. 31 (1915). • S. macrostachyum, abaxial epidermis of leaf blade: this project. • S. macrostachyum, T.S. of leaf blade with showing arm-cells: this project. Sclerodactylon macrostachyum. PCA mesophyll with arm cells. • TS leaf blade of S. macrostachyum: this project. Sclerodactylon macrostachyum.
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: 13th November 2017. delta-intkey.com/grass’.