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The grass genera of the world

L. Watson, T.D. Macfarlane, and M.J. Dallwitz

Bothriochloa Kuntze

From the Greek bothrion (a pit) and chloë (a grass), alluding to pitted lower glumes.

~ Dichanthium

Including Amphilophis Nash, Gymnandropogon (Nees) Duthie

Habit, vegetative morphology. Perennial; rhizomatous, or stoloniferous, or caespitose, or decumbent. Culms 15–200 cm high; herbaceous; branched above, or unbranched above. The branching if branched, simple, or fastigiate. Culm nodes hairy, or glabrous. Culm internodes solid. Young shoots intravaginal. The shoots aromatic, or not aromatic. Leaves not basally aggregated; non-auriculate. Leaf blades linear; narrow; flat; without cross venation; persistent; rolled in bud. Ligule present; an unfringed membrane to a fringed membrane; truncate, or not truncate. Contra-ligule absent.

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets. The spikelets of sexually distinct forms on the same plant; hermaphrodite and male-only, or hermaphrodite and sterile. The male and female-fertile spikelets mixed in the inflorescence. The spikelets overtly heteromorphic; all in heterogamous combinations. Plants exposed-cleistogamous, or chasmogamous. Apomictic, or reproducing sexually.

Inflorescence. Inflorescence of spicate main branches (many-jointed ‘racemes’), or paniculate (rarely: the lower ‘racemes’ sometimes branched again at the base); digitate, or subdigitate (the racemes often almost palmate, towards the culm tips), or non-digitate; spatheate, or espatheate; a complex of ‘partial inflorescences’ and intervening foliar organs, or not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes ‘racemes’; the spikelet-bearing axes usually with more than 10 spikelet-bearing ‘articles’. The racemes without spikelets towards the base. Spikelet-bearing axes solitary, or paired, or clustered; with very slender rachides; disarticulating; disarticulating at the joints. The pedicels and rachis internodes with a longitudinal, translucent furrow. ‘Articles’ linear; without a basal callus-knob; not appendaged; disarticulating transversely; densely long-hairy (often villous), or somewhat hairy, or glabrous. Spikelets mainly paired (with a terminal triplet); secund; sessile and pedicellate; consistently in ‘long-and-short’ combinations; in pedicellate/sessile combinations. Pedicels of the ‘pedicellate’ spikelets free of the rachis. The ‘shorter’ spikelets hermaphrodite. The ‘longer’ spikelets male-only, or sterile.

Female-sterile spikelets. The pedicels of the male or sterile pedicellate spikelets often villous. The lemmas awnless.

Female-fertile spikelets. Spikelets compressed dorsiventrally; falling with the glumes (and with the joint). Rachilla terminated by a female-fertile floret. Hairy callus present. Callus short; blunt.

Glumes two; more or less equal; long relative to the adjacent lemmas; hairy (towards the base), or hairless; glabrous, or scabrous; pointed, or not pointed (blunt or minutely bifid); awnless; very dissimilar (the lower bicarinate and often with a pit on the back, the upper narrower, naviculate). Lower glume two-keeled; convex on the back to flattened on the back; with a conspicuous pit, or not pitted; relatively smooth; 5–9 nerved. Upper glume 1–4 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; more or less equalling the female-fertile lemmas to decidedly exceeding the female-fertile lemmas; similar in texture to the female-fertile lemmas; not becoming indurated.

Female-fertile florets 1. Lemmas linear, produced into the awn; less firm than the glumes (reduced to a hyaline stipe); not becoming indurated; entire; awned. Awns 1; median; apical; geniculate; hairless (glabrous); much longer than the body of the lemma. Lemmas hairless; glabrous; non-carinate; without a germination flap; 1–3 nerved. Palea present, or absent; when present, very reduced; not indurated; nerveless. Lodicules present; 2; free; fleshy; glabrous. Stamens 1–3. Anthers about 1.5 mm long; not penicillate; without an apically prolonged connective. Ovary apically glabrous. Styles free to their bases. Stigmas 2; red pigmented.

Fruit, embryo and seedling. Fruit free from both lemma and palea; small; compressed dorsiventrally. Hilum short. Embryo large. Endosperm hard; without lipid; containing only simple starch grains. Embryo without an epiblast; with a scutellar tail; with an elongated mesocotyl internode. Embryonic leaf margins overlapping.

Seedling with a long mesocotyl. First seedling leaf with a well-developed lamina. The lamina broad; curved, or supine; 21–30 veined.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae present; intercostal. Intercostal papillae over-arching the stomata; consisting of one oblique swelling per cell. Long-cells similar in shape costally and intercostally; of similar wall thickness costally and intercostally. Mid-intercostal long-cells rectangular (long, narrow); having markedly sinuous walls. Microhairs present; panicoid-type; 38–66 microns long. Microhair apical cells 24–33 microns long. Microhair apical cell/total length ratio 0.5–0.64. Stomata common. Subsidiaries non-papillate; triangular. Intercostal short-cells absent or very rare. Costal short-cells conspicuously in long rows. Costal silica bodies ‘panicoid-type’; cross shaped, or butterfly shaped, or dumb-bell shaped, or nodular.

Transverse section of leaf blade, physiology. C4; XyMS–. PCR sheath outlines uneven. PCR cells with a suberised lamella. PCR cell chloroplasts with reduced grana; centrifugal/peripheral. Mesophyll with radiate chlorenchyma. Leaf blade adaxially flat (usually), or ‘nodular’ in section; with the ribs more or less constant in size (when present). Midrib conspicuous; with one bundle only, or having a conventional arc of bundles; with colourless mesophyll adaxially. Bulliforms present in discrete, regular adaxial groups, or not present in discrete, regular adaxial groups; in simple fans (or in irregular groups), or associated with colourless mesophyll cells to form deeply-penetrating fans. Many of the smallest vascular bundles unaccompanied by sclerenchyma. Combined sclerenchyma girders present; forming ‘figures’, or nowhere forming ‘figures’. Sclerenchyma all associated with vascular bundles.

Culm anatomy. Culm internode bundles in one or two rings, or in three or more rings.

Phytochemistry. Tissues of the culm bases with abundant starch. Leaves containing flavonoid sulphates (in at least some material of each of 6 species), or without flavonoid sulphates (at least sometimes, in 4 species).

Cytology. Chromosome base number, x = 10. 2n = 30, 40, 50, and 120. 2, 4, 5, 6, and 12 ploid. Chromosomes ‘small’.

Classification. Watson & Dallwitz (1994): Panicoideae; Andropogonodae; Andropogoneae; Andropogoninae. Soreng et al. (2015): Panicoideae; Andropogonodae; Andropogoneae; Anthistiriinae. 35 species.

Distribution, phytogeography, ecology. Warm regions.

Commonly adventive. Mesophytic; species of open habitats; glycophytic. Grassy places.

Economic aspects. Significant weed species: B. ischaemum, B. pertusa, B. saccharoides. Cultivated fodder: B. insculpta. Important native pasture species: B. bladhii, B. ewartiana, B. insculpta, B. ischaemum, B. pertusa, B. radicans, etc.

Hybrids. Intergeneric hybrids with Capillipedium, Dichanthium.

Rusts and smuts. Rusts — Puccinia. Taxonomically wide-ranging species: Puccinia nakanishikii, Puccinia graminis, Puccinia versicolor, ‘Uromycesclignyi, and Puccinia cesatii. Smuts from Ustilaginaceae. Ustilaginaceae — Sorosporium, Sphacelotheca, and Ustilago.

References, etc. Leaf anatomical: Metcalfe 1960; studied by us - B. macra (Steudel) Blake.

Illustrations. • B. bladhii: Gardner, 1952. • B. ewartiana: Gardner, 1952. • B. insculpta: Gibbs Russell et al., 1990. • Inflorescence detail (B. macra). Bothriochloa macra. ‘Pitted’ lower glumes. • Lowr glume detail (B. macra). Bothriochloa macra. ‘Pitted’ lower glume. • Detail of rachis segment (B. macra). Bothriochloa macra. Longitudinal translucent furrow. • Inflorescence detail (B. bladhii). • Spikelet and floret details (B. bladhii). • B. macra, TS of leaf blade: this project. Bothriochloa macra. Midrib region. • B. macra, T.S. leaf blade, electron micrograph: this project. Bothriochloa macra. C4 type NADP-ME.

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.’.