Aegopogon Humb. & Bonpl. ex Willd.
From the Greek aix (goat) and pogon (beard), referring to fascicles of awns.
Including Atherophora Steud., Hymenothecium Lag., Schellingia Steud.
Habit, vegetative morphology. Delicate annual. Culms 6–30 cm high; herbaceous. Leaves not basally aggregated; non-auriculate. Sheaths loose. Leaf blades linear; narrow; 1–2 mm wide; flat; without abaxial multicellular glands; without cross venation; persistent; a fringed membrane.
Reproductive organization. Plants bisexual, with bisexual spikelets; with hermaphrodite florets. The spikelets of sexually distinct forms on the same plant; hermaphrodite, male-only, and sterile. The male and female-fertile spikelets mixed in the inflorescence (in triads, the central member hermaphrodite, the laterals male or sterile). The spikelets overtly heteromorphic.
Inflorescence. Inflorescence a false spike, with spikelets on contracted axes (the main axis bearing triplets of spikelets with short flat pedicels, the triplets short-pedunculate, spreading, the rachis filiform); espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes disarticulating; falling entire (i.e. the triplets falling). Spikelets in triplets; secund (the triplets on one side of the axis); sessile and pedicellate, or subsessile and pedicellate; consistently in ‘long-and-short’ combinations; in pedicellate/sessile combinations, or unequally pedicellate in each combination (the central hermaphrodite spikelet sessile or subsessile, the reduced laterals pedicellate). The ‘shorter’ spikelets hermaphrodite. The ‘longer’ spikelets male-only, or sterile.
Female-sterile spikelets. The longer-pedicelled male or neuter spikelets reduced.
Female-fertile spikelets. Spikelets 2 mm long; compressed laterally, or not noticeably compressed, or compressed dorsiventrally (?); falling with the glumes (the triplets disarticulating, with the pointed basal stipe). Rachilla terminated by a female-fertile floret.
Glumes present; two; more or less equal; shorter than the spikelets; shorter than the adjacent lemmas; free; not pointed (apically notched); awned (via the extended midnerve); similar (membranous, truncate or notched, awned). Lower glume 1 nerved (?). Upper glume 1 nerved (?). Spikelets with female-fertile florets only; without proximal incomplete florets.
Female-fertile florets 1. Lemmas similar in texture to the glumes (membranous); not becoming indurated; incised; with a narrow, nerveless lobe outside each lateral awn; not deeply cleft; awned. Awns 3; median and lateral; the median similar in form to the laterals; continued from the nerve; non-geniculate (delicate); hairless (scabrous); much longer than the body of the lemma; entered by one vein. The lateral awns shorter than the median. Lemmas hairless; without a germination flap; 3 nerved. Palea present; relatively long (but somewhat shorter than the lemma); apically notched; awned (two-awned); textured like the lemma; not indurated; 2-nerved. Lodicules present; 2; fleshy; glabrous. Stamens 3. Anthers small. Ovary glabrous. Stigmas 2.
Fruit, embryo and seedling. Fruit small (about 1.7 mm long in A. bryophylus); fusiform, or ellipsoid; compressed laterally. Hilum short. Pericarp fused. Embryo large; 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 present; intercostal. Intercostal papillae not over-arching the stomata (for the most part); consisting of one oblique swelling per cell (large). Mid-intercostal long-cells rectangular; having straight or only gently undulating walls. Microhairs present; chloridoid-type. Microhair apical cell wall of similar thickness/rigidity to that of the basal cell. Microhair basal cells 30 microns long. Stomata common. Subsidiaries non-papillate; dome-shaped (sometimes approaching parallel). Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; not paired (solitary); not silicified. Intercostal silica bodies absent to imperfectly developed. Costal short-cells conspicuously in long rows. Costal silica bodies present and well developed; confined to the central file(s) of the costal zones to present in alternate cell files of the costal zones; ‘panicoid-type’; cross shaped to dumb-bell shaped.
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 absent. Leaf blade with distinct, prominent adaxial ribs, or ‘nodular’ in section. Midrib not readily distinguishable; with one bundle only. Bulliforms present in discrete, regular adaxial groups; in simple fans (the large median cell of each group deeply inserted in the mesophyll). All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present (with the main bundles); forming ‘figures’ (the main bundles with anchors). Sclerenchyma all associated with vascular bundles.
Taxonomy. Chloridoideae; main chloridoid assemblage.
Distribution, ecology, phytogeography. 3 species; Southern U.S.A. to Argentina.
Holarctic, Paleotropical, and Neotropical. Madrean. Indomalesian. Papuan. Caribbean, Venezuela and Surinam, and Andean.
Rusts and smuts. Rusts — Puccinia. Smuts from Ustilaginaceae. Ustilaginaceae — Ustilago.
References, etc. Leaf anatomical: this project.
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).