Eriochrysis laxa Swallen (1966: 89)

Welker, Cassiano Aimberê Dorneles, Longhi-Wagner, Hilda Maria & Souza-Chies, Tatiana Teixeira De, 2012, New record for Eriochrysis (Poaceae: Andropogoneae) in the State of Rio Grande do Sul, Brazil, and a key to the species of Eriochrysis in Brazil, Phytotaxa 71 (1), pp. 1-4 : 1-3

Eriochrysis laxa Swallen (1966: 89) ( Fig. 1D–G )

Type:— BRAZIL. Minas Gerais: Lavras , in wet ground near streamlet, 5 March 1925, Agnes Chase 8729 (holotype US- 1256173 photo!; isotype MO-925236 photo!) .

Perennial, caespitose, (125–)140–190(–215) cm high, nodes pilose. Leaf sheaths glabrous, less commonly sparsely pilose near the apex; blades glabrous on abaxial surface, densely pilose on adaxial surface, with dense tufts of trichomes 4–8 mm long at the base of the adaxial surface behind the ligule; blades of innovations 25–50(–68) cm long, subfiliform below, 2–4 mm wide above, those of the culm (18–) 35–70 cm long, 5–10 mm wide; ligule membranous-ciliate, 1–1.5 mm long. Inflorescence contracted to subcontracted, (12–) 16–32 cm long, bearing numerous alternate racemes on a central axis, the lower racemes placed distantly; racemes differentiated into nodes and internodes, disarticulating at the nodes, sparsely pilose, spikelets clearly visible among the golden-brown trichomes. Spikelets paired at each node of the rachis, one sessile and one pedicelled, the pedicelled spikelet falling off first at maturity, the sessile falling off together with a rachis internode and the pedicel. Sessile spikelet (2.2–)2.5–3(–3.5) mm long, obovate, awnless, with bisexual flower; glumes chartaceous, the lower glume glabrous on back, with trichomes 1–2 mm long on margins, with the apex rounded to obtuse, the upper glume ciliate in the upper half of the margins, with the apex acute to subacute; lemmas hyaline; callus hairs reaching 1/2 to 2/3 of the length of the spikelet. Pedicelled spikelet 1.7–2.5 mm long, similar to the sessile, but with pistillate flower. Caryopsis 0.7–1 mm long.

Distribution and habitat: — Colombia, Bolivia, Paraguay, Argentina, and Brazil ( Swallen 1966). In Brazil, it occurs from the States of Goiás to Santa Catarina ( Swallen 1966, Smith et al. 1982) and in Rio Grande do Sul, in marshlands and wet grasslands.

Eriochrysis laxa is morphologically similar to E. cayennensis and E. villosa , distinguished mainly by the less pilose inflorescences, resulting in clearly visible spikelets among the trichomes ( Fig. 1E ), and the obovate sessile spikelets ( Fig. 1F–G ). Eriochrysis cayennensis and E. villosa have densely pilose inflorescences with spikelets hidden among the trichomes, and ovate to elliptic sessile spikelets. Furthermore, the apex of the lower glume is rounded to obtuse in E. laxa ( Fig. 1G ), but truncate and trilobed in E. cayennensis ( Fig. 1A ), and acute to subacute, not lobed ( Fig. 1I ) or with inconspicuous lobes ( Fig. 1J ) in E. villosa .

Eriochrysis holcoides and E. warmingiana ( Hackel 1883: 254) Kuhlmann (1922: 29) differ from E. laxa by the lanceolate to elliptic sessile spikelets and the lower glume with an acute or acuminate apex ( Fig. 1C, 1K ). Eriochrysis filiformis ( Hackel 1889: 29) Filgueiras (1997: 231) differs from E. laxa and the other Brazilian species of the genus by having a pair of spikelets consisting of short- and long-pedicelled spikelets ( Fig. 1B ). Note that because of this characteristic, E. filiformis was initially erroneously placed in the tribe Paniceae ( Filgueiras 1997) . Eriochrysis filiformis also has narrower leaf blades than the other species.

Killeen (1990) described Eriochrysis × concepcionensis Killeen (1990: 157) as a hybrid between E. laxa and E. cayennensis , based on a single population with intermediate morphology found in Santa Cruz ( Bolivia) in the same habitat as both parental species. We also found some specimens with intermediate morphology between E. laxa and E. cayennensis in a marshland in Rio Grande do Sul ( Brazil) together with specimens of the two latter species. These plants, here treated as E. aff. laxa and represented by the specimen Welker 487 (ICN), have obovate sessile spikelets as E. laxa and densely pilose inflorescences as E. cayennensis . The apex of the lower glume is rounded as E. laxa , but has inconspicuous lobes ( Fig. 1H ). These individuals are likely natural hybrids between these species. We are conducting molecular and cytogenetic studies to examine this issue.

Figures

FIGURE 1. Morphological details of the Eriochrysis species. A. E. cayennensis, lower glume of the sessile spikelet (Longhi-Wagner & Welker 10781, ICN). B. E. filiformis, pair of spikelets (Câmara & Filgueiras 30, ICN). C. E. holcoides, lower glume of the sessile spikelet (Longhi-Wagner & Welker 10731, ICN). D–G. E. laxa (Welker 489, ICN). D. habit. E. inflorescence. F. pair of spikelets. G. lower glume of the sessile spikelet. H. E. aff. laxa, lower glume of the sessile spikelet (Welker 487, ICN). I–J. E. villosa. I. lower glume of the sessile spikelet (Welker 328, ICN). J. lower glume of the sessile spikelet (Welker 182, ICN). K. E. warmingiana, lower glume of the sessile spikelet (Filgueiras 1902, ICN). Illustrations by Anelise Scherer and Cassiano A. D. Welker.