Sporobolus nesiotioides Longhi-Wagner, R.J.V. Alves & Nílber, 2013

Longhi-Wagner, Hilda M., Alves, Ruy J. V., Da Silva, Nílber G. & Guimarães, Alessandra R., 2013, A new species of Sporobolus (Poaceae, Chloridoideae) from Trindade Island, Brazil, with comments on the distribution of the genus in the South Atlantic, Phytotaxa 144 (1), pp. 13-21 : 13-18

Sporobolus nesiotioides Longhi-Wagner, R.J.V. Alves & Nílber sp. nov., Fig. 1–4 .

Type:— BRAZIL, Trindade Island , South Atlantic, 380 m elevation, 20 o 30’ 05.92” S, 29 o 20’ 10.17” W, 28 February 2012, R. J. V . Alves 8831 & N. G . Silva (holotype R!, isotype ICN!) .

Sporobolus nesiotioides S. duro affinis , sed differt precipue amplitudine magna, paniculis patentioribus et laminis foliorum filiformibus longioribus angustioribus.

Sporobolus nesiotioides is close to S. durus from which it differs mainly by the taller habit, the more lax panicle, and by the filiform leaf blades, longer and narrower than in S. durus .

Caespitose perennial herb, 70–90 cm tall ( Figs. 1 , 3 ), with a short rhizome. Leaf sheaths glabrous, 3–5 mm wide, conspicuously wider than the leaf blades; ligule 0.2–0.3 mm long, membranous-ciliate, truncate; leaf blades 30–60 cm × 1.2–1.5 mm, conduplicate or convolute, 0.3–0.6 mm in diameter, long-acuminate, adaxial surface scabrid, margins densely scabrid, apex of the leaf-sheath with a tuft of trichomes 4–5 mm long. Peduncle to 80 cm long. Panicle open to lax ( Fig. 2 ), 5.5–17 cm long, primary branches verticillate, less often subverticillate, spikelets clustered mainly at the upper two thirds of the primary branches; rhachis and peduncle glabrous. Spikelets pedicelled, 3–3.5 mm long, with one anthecium, laterally compressed; glumes unequal, acute, membranous, initially persistent in the inflorescence, deciduous at maturity, dehiscing after the anthecium; lower glume nerveless, membranous, 1.3–1.5(–2) mm long, about half the length of the upper glume; upper glume 1-nerved, 3–3.5 mm long, reaching the anthecium; lemma 2.8–3.2 mm long, 1-nerved, acute; palea 2.7–3 mm long, 1-nerved, obtuse. Stamens 1–2. Caryopsis elliptic, 1–1.3 × 0.6 mm.

Leaf anatomy:—Transverse section of lamina c-shaped (convolute), 7-nerved. The leaf blades present a typical Kranz anatomy of the C 4 PCK type (sensu Hattersley 1986) and XyMS+, with cells between the metaxylem elements and adjacent chlorenchymatous tissue, according to Hattersley & Watson (1976). Adaxial surface with ribs and furrows; furrows about ½ as deep as the leaf thickness; epidermis unistratified; vascular bundles in the median layer of the blade; primary vascular bundles rectangular, secondary vascular bundles elliptic, with a double sheath; outer Kranz parenchyma sheath with large and thin walled cells, with specialized chloroplasts of centripetal location, suggesting that it belongs to the NAD-ME biochemical subtype according to Hattersley (1986) and Peterson & Herrera-Arrieta (2001); outer Kranz sheath interrupted by sclerenchyma girders toward both surfaces; inner sheath with small and thick walled cells, entire; tertiary vascular bundles round, the outer sheath entire, not interrupted, the inner sometimes inconspicuous. Chlorenchyma cells surround the vascular bundles and are continuous between the bundles, in a loose arrangement. Bulliform cells in small groups, generally 3, in adaxial furrows and between the tertiary vascular bundles ( Fig. 4 ).

The leaf anatomy of S. durus was analyzed using leaves received from K and P Herbaria, from collections made in 1829 and 1889, respectively. Even though this analysis was difficult due to the age of the material, it is possible to confirm that S. durus presents a leaf anatomy comparable to S. nesiotioides : both species present a unistratified epidermis on both faces, covered by a thickened cuticle. They differ mainly by S. durus having a larger quantity of sclerenchyma, so its leaves are more rigid than in S. nesiotioides . Sclerenchymatic bundles associated with the minor veins, just below the epidermis, in both faces of the leaf, are copious in S. durus and do not occur in S. nesiotioides . The major veins bear a sclerenchyma sheath which has lateral projections on both faces, which is more expressive in S. durus . Both species share Kranz anatomy, with S. nesiotioides displaying a centripetal chloroplast arrangement. In S. durus we observed chloroplasts in several positions but this may be due to the age of the material.

Distribution and habitat:— Sporobolus nesiotioides is known only from Trindade Island, South Atlantic ( Brazil) where it forms a contiguous herbaceous cover of dense and uniform tussocks ( Fig. 3 ) on flat volcanic tuff summits from 300 to 500 m elevation. Photos of Martin Vaz main island, ca. 50 km east of Trindade, taken by the Brazilian ornithologist Dr. Leandro Bugoni, strongly suggest that S. nesiotioides also occurs on the main island of that Archipelago. It was collected fertile for the first time in 2012, probably due to prior overgrazing by feral goats which were eradicated in 2005 ( Silva & Alves 2011).

Etymology:—“ Nesiotis” has its root in Ancient Greek nisiótis, originally referring to the people of Cephalonia Island. Later, the term came to be used in taxonomy with the meaning of “insular”, in general. Besides the insular habitat, the choice of this name is also related to the fact that S. nesiotioides has been observed by the collectors since 1994 in sterile condition, leading to a historical confusion with Bulbostylis nesiotis ( Hemsley 1884: 130) Clarke (1908: 27) , a sympatric endemic sedge which is vegetatively quite similar. Therefore the suffix oides, meaning “looking like”.

Paratypes:— BRAZIL, Ilha da Trindade , Platô do Desejado, 18 February 2013, R. J. V . Alves 8827 & N. G . Silva (paratype R!, isoparatype RB!) .

Additional material of S. caespitosus examined:— Ascension Island, August 1886, H. J . Gordon 123 (photo K!) .

Additional material of S. durus examined:— Ascension Island, 1829, d´Urville 32 ( P02307222 !, P02649728 !, P02649729 !, P03652320 !) ; Ascension Island, August 1886, H. J . Gordon no. 125 (photo K!) .

Additional material of S. virginicus examined:— Brazil, Trindade Island , summit of Pico Desejado, 18 February 2013, R. J. V . Alves 8827 and N. G . Silva (R!).

Figures

FIGURE 1. Sporobolus nesiotioides (the holotype) A. Lateral view of spikelet showing the two glumes, lemma and palea; B. Glumes in lateral view; C. Caryopsis; D. Habit. E. Transverse section of the leaf showing the naturally convolute position. (Illustrations: A–C by H. M. Longhi-Wagner and Anelise Scherer; D–E by R. J. V. Alves).

FIGURE 2. Sporobolus nesiotioides: detail of the lax panicle of the holotype.

FIGURE 3. Natural population of S. nesiotioides on Trindade Island. (Photo: N.G. Silva).

FIGURE 4. A, C, E. Sporobolus nesiotioides, R.J.V. Alves 8831 & N. G. Silva (R!); B, D. Sporobolus durus, d´Urville 32 (P!), F. Sporobolus durus, C. H. J. Gordon 125 (K!); Ep. Epidermis; Ks. Kranz sheath; P. Parenchyma; Ph. Phloem; Sb. Sclerenchymatic bundle; Ss. Sclerenchymatic sheath; X. Xylem. Scale bars: A. (10µm); B. (50µm); C–F (5µm). (Photos and plate: A.R. Guimarães).