Sclerodactylon Stapf
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; a fringe of hairs (short, dense). Contra-ligule absent.
Reproductive organization. Plants bisexual, 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 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).
Taxonomy. Chloridoideae; main chloridoid assemblage.
Distribution, ecology, phytogeography. 1 species; Madagascar, Aldabra, Assumption. Xerophytic (extreme); species of open habitats; halophytic (coral rocks, salt pans, mangrove swamps).
Paleotropical. Madagascan.
References, etc. Leaf anatomical: this project.
Special comments. Rows of ‘crypts’ containing crystalline material (NaCl?) occur within the grooves if the leaf blade.
Illustrations. • Abaxial epidermis of leaf blade. • Transverse section of leaf blade. Sclerodactylon macrostachyum. PCA mesophyll with arm cells. • Transverse section of leaf blade. Sclerodactylon macrostachyum.
Cite this publication as: Watson, L., and Dallwitz, M. J. (1992 onwards). ‘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.’ http://biodiversity.uno.edu/delta/. Version: 18th August 1999. Dallwitz (1980), Dallwitz, Paine and Zurcher (1993 onwards, 1998), and Watson and Dallwitz (1994), and Watson, Dallwitz, and Johnston (1986) should also be cited (see References).
