The grass genera of the world
Including Rhachidospermum Vasey
Habit, vegetative morphology. Perennial; stoloniferous and caespitose. Culms 50 cm high; herbaceous. Leaves not basally aggregated; non-auriculate. Leaf blades narrow; 2–4 mm wide (glabrous); flat, or rolled (involute); without abaxial multicellular glands; without cross venation; disarticulating from the sheaths. Ligule a fringed membrane (the membrane very short, with a conspicuous fringe).
Reproductive organization. Plants monoecious with all the fertile spikelets unisexual, or dioecious; without hermaphrodite florets. The spikelets of sexually distinct forms on the same plant (when monoecious), or all alike in sexuality (when dioecious); female-only, or male-only. The male and female-fertile spikelets in different inflorescences.
Inflorescence. Inflorescence with male spikelets in long-peduncled, dorsiventral spikes, with a spikelet terminating the rachis and the spikes in axillary fascicles (J. pilosa) or groups of 1–3 (J. straminea); the female spikelets thornlike, each with an associated prophyll and spathe, these units in axillary umbels (J. pilosa, cf. female Spinifex) or in small spiny clusters (J. straminea); spatheate (the female spikelet clusters with umbels of spathes), or espatheate (the male inflorescences). Spikelets associated with bractiform involucres (i.e., the spathes); secund (males), or not secund (females).
Female-sterile spikelets. Male spikelets sessile, disarticulating above the glumes, their 3–5 fertile florets with 2 large fleshy lodicules and 3 stamens. The male spikelets with glumes; without proximal incomplete florets; 3–7 floreted. Male florets 3–5; 3 staminate.
Female-fertile spikelets. Spikelets so unconventional (as to be only dubiously interpretable as spikelets rather than spikes); 20–30 mm long, or 40–50 mm long; not noticeably compressed (cylindrical, thorn-like); falling whole; not disarticulating between the florets. Rachilla prolonged beyond the uppermost female-fertile floret (as a subulate point, which becomes a thorn at maturity); hairless; the rachilla extension with incomplete florets. Hairy callus absent.
Glumes absent. Spikelets with incomplete florets. The incomplete florets distal to the female-fertile florets. The distal incomplete florets 1–3; merely underdeveloped.
Female-fertile florets 2–4(–8) (completely embedded in the thick, spongy, cylindrical rachilla). Lemmas forming a tube around the floret, adnate to and embedded in the rachilla for most of their length, with an apical pore through which the stigmas protrude; becoming indurated; awnless (?); hairless; glabrous; non-carinate. Palea present (adaxially, but detected only on sectioning the spikelet); (in sections) conspicuous but relatively short (not much longer than the ovary); awnless, without apical setae; thinner than the lemma (very flimsy); not indurated; nerveless. Lodicules absent. Stamens 0 (reduced to three vestiges). Ovary apically glabrous. Styles fused (ovary attenuate into the long style). Stigmas 2 (long, exserted); red pigmented, or brown (?).
Fruit, embryo and seedling. Fruit ellipsoid. Embryo 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 (and pitted, with pits also in the outer walls). Microhairs present; more or less spherical; clearly two-celled; chloridoid-type (basal cell embedded in J. straminea, normal in J. pilosa). Microhair apical cell wall of similar thickness/rigidity to that of the basal cell. Microhairs 30–39 microns long (J. pilosa), or 18–21 microns long (J. straminea). Microhair basal cells 6 microns long. Microhairs 18.6–21.6 microns wide at the septum (J. pilosa), or 13.5–16.5 microns wide at the septum (J. straminea). Microhair total length/width at septum 1.4–2.1. Microhair apical cells (10.5–)12–16.5(–17.4) microns long. Microhair apical cell/total length ratio 0.32–0.52, or 0.64–0.67. Stomata common; 43.5–48 microns long (J. pilosa), or 28.5–33 microns long (J. straminea). Subsidiaries high dome-shaped (J. straminea), or parallel-sided and dome-shaped (J. pilosa, where the domes are mainly low). Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs; silicified. Intercostal silica bodies present and perfectly developed; saddle shaped (tiny), or crescentic. Costal short-cells predominantly paired. Costal silica bodies present throughout the costal zones; crescentic (predominating), or saddle shaped (a few, more or less imperfect).
Transverse section of leaf blade, physiology. Lamina mid-zone in transverse section open.
C4; XyMS+. PCR sheaths of the primary vascular bundles complete. PCR sheath extensions present. Maximum number of extension cells 2. Mesophyll traversed by columns of colourless mesophyll cells. Leaf blade adaxially flat. Midrib conspicuous (with a large abaxial anchor-shaped strand in J. straminea), or not readily distinguishable; with one bundle only. Bulliforms present in discrete, regular adaxial groups; associated with colourless mesophyll cells to form deeply-penetrating fans (these linked with traversing columns of colourless cells). All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders absent (most bundles with scant abaxial strands, but many altogether lacking adaxial sclerenchyma). Sclerenchyma all associated with vascular bundles. The lamina margins with fibres.
Classification. Watson & Dallwitz (1994): Chloridoideae; main chloridoid assemblage. Soreng et al. (2015): Chloridoideae; Cynodonteae. 2 species.
Distribution, phytogeography, ecology. California to Central America.
Xerophytic; species of open habitats; halophytic, or glycophytic. Sandy places, coastal dunes and mud flats.
References, etc. Morphological/taxonomic: Weatherwax 1939. Leaf anatomical: Metcalfe 1960; studied by us - J. pilosa (Presl) Scribn., J. straminea Fourn.
Special comments. Fruit data wanting. Illustrations. • J. straminea: Ann. Miss. Bot. Gard. 30 (1943). • J. straminea, 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’.