Andropogon, Linnaeus (1753:, 1045

Nagahama, Nicolás, Anton, Ana M. & Norrmann, Guillermo A., 2013, Andropogon × guaraniticus (Andropogoneae, Poaceae): a name for a natural hybrid from northeastern Argentina, Phytotaxa 129 (1), pp. 53-58 : 53-56

Andropogon × guaraniticu s Nagahama & Norrmann, nothosp. nov., Figs. 1 , 2

Type:— ARGENTINA. Corrientes: San Roque, Ruta 12, 30 km S de San Roque , 2 January 1996, 28°49’56”S, 58°43’45”W, 213 m, Norrmann 227 (holotype CTES!; isotype CORD) .

Andropogon × guaraniticus is distinguished from A. macrothrix by its longer hairs on the pedicel and the callus of the sessile spikelet, narrower apex of the rachis internodes, and a shorter awn. It is easily distinguished from A. selloanus by its long awns, which are lacking in A. selloanus .

Plants perennial, cespitose, culms 58.1–96.7 cm tall, nodes 5–7, glabrous. Innovations intravaginal, vernation conduplicate. Leaf sheaths generally longer than the internodes in the basal region and shorter than the internodes in the distal region, glabrous; blades 15.7–47.5 × 0.26–0.54 cm, straight, usually flat, the basal ones with marginal trichomes 3.2–5.3 mm long, glabrous on both surfaces, margins scabrous towards the apex; apex generally subobtuse or rarely obtuse navicular; ligule 0.43–0.85 mm long, obtuse, membranousciliate; apex denticulate. Inflorescence scarcely branched, 28.1–75.1 cm long, composed of both terminal and axillary inflorescence units, these units 5–7.7 cm long, with 2–5 racemes, equal or subequal in length, conjugate or subdigitate, exserted or partially enclosed by the spatheole; peduncle 9.4–20.8 cm long; spatheoles 7.4–11 cm long. Pedicels and rachis internodes linear, pedicels 3.8–4.2 mm long, internodes 3.1– 4.4 mm long, apex of the rachis internodes cup-shaped, 0.61–0.77 mm wide; both with hairs 7.8–11.3 mm long. Sessile spikelets (in the middle or proximal pair) perfect, 4.2–4.8 × 0.6–1 mm, awned; sessile spikelets callus pubescent, hairs 3.1–4.5 mm long. Lower glume 4–5.2 × 1–1.4 mm, slightly concave, lanceolate, chartaceous, margins glabrous, 2–nerved, scabrous on the upper portion of the keels; upper glume 3.5–4.3 × 0.9–1.3 mm, chartaceous, margins ciliate towards the apex, 3–nerved, the lateral nerves tenuous, apex acute or briefly awned. Lower lemma 2.8–3.5 × 0.5–0.8 mm, bicarinate, lanceolate, hyaline, margins glabrous at base, ciliate towards the apex, 2–nerved, acuminate; palea absent; upper lemma 2.6–2.9 × 0.5–0.8 mm, hyaline, ciliate on the margins towards the apex, 3–nerved, acute, awned, awn 11.3–15 mm long; palea 0.8–2.2 × 0.3– 0.5 mm, hyaline, margins glabrous at the base, ciliate towards the apex, 0–nerved, sub-obtuse. Lodicules 2, 0.5–0.7 mm long, glabrous. Stamens 3, anthers 1–1.6 mm long, yellow. Caryopsis not seen. Distal sessile spikelets reduced 1.5–2.5 × 0.2–0.4 mm long. Pedicellate spikelets vestigial, 1.8–2.6 × 0.2–0.4 mm.

Distribution and habitat:— Andropogon × guaraniticus is known from the San Roque Department in Corrientes, Argentina. It grows mainly on the boundaries of populations of A. selloanus on sandy soils in open disturbed places about 200–300 m elevation, generally on road margins. Andropogon selloanus grows from Mexico to Argentina, usually on dry and sandy soils or on wet soils in the Pantanal, central and southern Brazil. Andropogon macrothrix grows in Uruguay, northeast Argentina, Paraguay, east Bolivia and south and central Brazil, on edges of streams, low swampy areas or wet soils.

Etymology:—The epithet refers to the Guarani Indians, a group of indigenous peoples of southern South America.

and measured using digital calipers (Electronic IP65, 797 B Series, Starrett®).

Notes:— Andropogon selloanus was dominant at the collection site of A. × guaraniticus, while A. macrothrix grew in isolated low swampy areas on the side of the road. An on-site estimate of the relative numbers of individuals of the two species was ca. 100:1 for A. selloanus and A. macrothrix , respectively. Andropogon macrothrix and A. selloanus are diploids (2 n = 2 x = 20, Norrmann 1985) and all hybrids obtained between them were also diploids (Galdeano & Norrmann 2000). These authors, based on the meiotic chromosome behavior and seed-set observations, confirmed the sterility of A. × guaraniticus. Therefore, these interspecific hybrids have been found only in the sympatric areas of the parental species, where the F 1 is formed.

Figures

FIGURE 1. Andropogon × guaraniticus. A. Habit. B. Detail of ligule. C. Unit of inflorescence. D. Middle or proximal pair of spikelets. E. Distal pair of spikelets. F–J. Sessile spikelet. F.Spikelet, dorsal view. G. Upper lemma. H. Lower lemma. I. Upper palea. J. Detail of lodicules, stigma and stamens. Only two of the three stamens were drawn. A–J. Drawn by Laura Ribulgo from the holotype (Norrmann 227).

FIGURE 2. Morphological comparison between A. macrothrix (Norrmann 93), A. selloanus (Norrmann 99) and A. × guaraniticus (Norrmann 227, holotype). A. Detail of ligule. B. Unit of inflorescence. C. Middle or proximal pair of spikelets. D. Distal pair of spikelets. A–D. Drawn by Laura Ribulgo.