Heteropogon Pers.
From the Greek heteros (different) and pogon (beard), re awned female-fertile and awnless male-fertile spikelets.
Including Spirotheros Raf.
Habit, vegetative morphology. Annual, or perennial; caespitose. Culms 20–100 cm high; herbaceous; branched above, or unbranched above. Culm nodes glabrous. Culm internodes solid. Leaves not basally aggregated; non-auriculate. Sheath margins free. The sheaths keeled. Leaf blades linear; narrow; flat; without cross venation; persistent; a fringed membrane.
Reproductive organization. Plants bisexual, with bisexual spikelets; with hermaphrodite florets, or without hermaphrodite florets. The spikelets of sexually distinct forms on the same plant (heterogamous, but only in the upper parts of the raceme); hermaphrodite, male-only, and sterile, or female-only, male-only, and sterile; overtly heteromorphic; in both homogamous and heterogamous combinations (lower pairs homogamous and homomorphic, male or sterile). Apomictic, or reproducing sexually.
Inflorescence. Inflorescence a single raceme, or paniculate (the single ‘racemes’ sometimes in false panicles); spatheate, or espatheate; a complex of ‘partial inflorescences’ and intervening foliar organs (when having axillary fascicles), or not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes ‘racemes’ (of several to many joints); solitary; disarticulating; disarticulating at the joints (between the heterogamous upper spikelet pairs). ‘Articles’ linear; disarticulating obliquely. Spikelets paired; secund; consistently in ‘long-and-short’ combinations; in pedicellate/sessile combinations (but the pedicel reduced to a short stump, the spikelet being supported on a long, slender callus). Pedicels of the ‘pedicellate’ spikelets free of the rachis. The ‘shorter’ spikelets hermaphrodite (in upper regions of spike-like panicles only), or female-only. The ‘longer’ spikelets male-only, or sterile.
Female-sterile spikelets. The pedicellate male or sterile spikelets larger, with a pedicel-like callus (the true pedicel represented by a stump); awnless, dorsally flattened, rather asymmetric. G1 herbaceous, many nerved, winged above. The male spikelets with glumes. The lemmas awnless.
Female-fertile spikelets. Spikelets not noticeably compressed to compressed dorsiventrally (subterete); falling with the glumes. Rachilla terminated by a female-fertile floret. Hairy callus present. Callus long; pointed.
Glumes two; more or less equal; long relative to the adjacent lemmas; hairy; without conspicuous tufts or rows of hairs; awnless; very dissimilar (the upper with deep longitudinal grooves). Lower glume not two-keeled; convex on the back; not pitted; relatively smooth, or tuberculate; 5–9 nerved. Upper glume 3 nerved. Spikelets with incomplete florets. The incomplete florets proximal to the female-fertile florets. Spikelets with proximal incomplete florets. The proximal incomplete florets 1; epaleate; sterile. The proximal lemmas awnless; 0 nerved; similar in texture to the female-fertile lemmas (hyaline); not becoming indurated.
Female-fertile florets 1. Lemmas stipitate-cartilaginous below, produced into the awn; less firm than the glumes (hyaline); not becoming indurated; entire; awned. Awns 1; median; apical; geniculate; hairy; much longer than the body of the lemma. Lemmas non-carinate; 3 nerved. Palea present, or absent; when present, very reduced; nerveless. Lodicules present, or absent; when present, 2; free; fleshy; glabrous. Stamens 0–3. Anthers not penicillate. Ovary glabrous. Styles free to their bases. Stigmas 2; red pigmented.
Fruit, embryo and seedling. Fruit free from both lemma and palea; longitudinally grooved (channelled on one side); compressed dorsiventrally. Hilum short. Embryo large. Endosperm containing only simple starch grains. Embryo without an epiblast; with a scutellar tail; with an elongated mesocotyl internode. Embryonic leaf margins overlapping.
First seedling leaf with a well-developed lamina. The lamina broad; curved; 21–30 veined.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae present (e.g. H. contortus), or absent (e.g. H. triticeus). Intercostal papillae consisting of one oblique swelling per cell (in H. contortus). Long-cells of similar wall thickness costally and intercostally. Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; panicoid-type; 61.5–82 microns long; 7.2–9.6 microns wide at the septum. Microhair total length/width at septum 6.4–8.8. Microhair apical cells 24–38 microns long. Microhair apical cell/total length ratio 0.41–0.51. Stomata common; 42–45 microns long. Subsidiaries triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs, or not paired (many solitary, some twos, some short rows - being an unusual feature in Poaceae); not silicified. Costal short-cells conspicuously in long rows. Costal silica bodies ‘panicoid-type’; cross shaped to dumb-bell shaped.
Transverse section of leaf blade, physiology. C4; XyMS–. PCR sheath outlines even (the walls thick). PCR sheath extensions absent. PCR cells with a suberised lamella. PCR cell chloroplasts with reduced grana; centrifugal/peripheral. Mesophyll with radiate chlorenchyma; traversed by columns of colourless mesophyll cells (in places, apparently, in H. triticeus), or not traversed by colourless columns. Leaf blade adaxially flat (the furrows scarcely detectable). Midrib conspicuous; having a conventional arc of bundles; with colourless mesophyll adaxially (e.g. in H. triticeus), or without colourless mesophyll adaxially (e.g. in H. contortus). Bulliforms present in discrete, regular adaxial groups; associated with colourless mesophyll cells to form deeply-penetrating fans (sometimes linked with traversing columns of colourless cells, or in places irregularly grouped); associating with colourless mesophyll cells to form arches over small vascular bundles (in places,in H. triticeus), or nowhere involved in bulliform-plus-colourless mesophyll arches. Many of the smallest vascular bundles unaccompanied by sclerenchyma. Combined sclerenchyma girders present; nowhere forming ‘figures’. Sclerenchyma all associated with vascular bundles.
Culm anatomy. Culm internode bundles scattered.
Phytochemistry. Leaves without flavonoid sulphates (2 species).
Cytology. Chromosome base number, x = 10 and 11. 2n = 20, 22, 40, 44, 50, 60, and 80. 2, 4, 6, and 8 ploid.
Taxonomy. Panicoideae; Andropogonodae; Andropogoneae; Andropogoninae.
Distribution, ecology, phytogeography. 7 species; tropical. Mesophytic to xerophytic; species of open habitats; glycophytic. Dry places, often on poor soils.
Holarctic, Paleotropical, Neotropical, Cape, and Australian. Boreal, Tethyan, and Madrean. African, Madagascan, Indomalesian, and Neocaledonian. Euro-Siberian and Atlantic North American. Mediterranean and Irano-Turanian. Saharo-Sindian, Sudano-Angolan, West African Rainforest, and Namib-Karoo. Indian, Indo-Chinese, Malesian, and Papuan. Caribbean, Central Brazilian, and Andean. North and East Australian. European. Southern Atlantic North American and Central Grasslands. Sahelo-Sudanian, Somalo-Ethiopian, South Tropical African, and Kalaharian. Tropical North and East Australian.
Rusts and smuts. Rusts — Puccinia. Taxonomically wide-ranging species: Puccinia versicolor and ‘Uromyces’ clignyi. Smuts from Ustilaginaceae. Ustilaginaceae — Sorosporium, Sphacelotheca, and Tolyposporium.
Economic importance. Significant weed species: H. contortus (with needle-sharp, penetrative callus). Important native pasture species: H. contortus.
References, etc. Leaf anatomical: Metcalfe 1960; this project.
Illustrations. • Inflorescence, spikelet. • General aspect. • Inflorescence detail. Heteropogon contortus. • Leaf blade transverse section. • Leaf blade transverse section
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).
