Grossera angustifolia Barberá & Riina, 2015

Barberá, Patricia, Riina, Ricarda & Velayos, Mauricio, 2015, A new species of Grossera (Euphorbiaceae) from Equatorial Guinea, Phytotaxa 221 (2), pp. 175-180 : 175-178

Grossera angustifolia Barberá & Riina , sp. nov. ( Fig. 1 & Fig. 2B–C )

The species is similar to Grossera paniculata Pax but it differs from the latter mainly in having shorter petioles and narrowly elliptic leaves that are spirally arranged. Grossera angustifolia has also smaller inflorescences and fruits than G. paniculata .

Type:— EQUATORIAL GUINEA. Litoral: Bata-Senye, estrada km 40, chegada a Senye á ponte sobre Rio Benito , 24 October 1991, M. Carvalho 4909 (holotype MA!; isotypes K!, L!, MA!, MO!) .

Shrubs 1–2 m tall; branches alternate, glabrous; leaves spirally arranged along branches. Leaf lamina 2.8–15 × 0.5– 2 cm, narrowly elliptic, equal-sided, base cuneate, with two glands at the junction with the petiole, very slightly glandulous-dentate from the middle to the upper part, apex acuminate, sometimes rounded, with a tip 2–7(–9) mm long, 7–11 pairs of lateral nerves, glabrous adaxially and abaxially, without glandular dots; petiole 0.3–0.8 cm long, glabrous, with pulvini, the apical pulvinus 1–1.4 mm long or sometimes absent, the basal pulvinus 1–1.7 mm long; stipules 0.6–1.5 mm long, lanceolate, deciduous, leaving small scars. Inflorescence paniculate, terminal. Male inflorescence 11–22 × (6–) 10–12 cm; main axis strigulose to puberulous, with appressed, antrorse hairs; bracts ovate to oblanceolate, acute, sometimes foliaceous, (1.2–)1.6–5.7(–11.7) × 1–1.8 mm, puberulous, with scattered hairs up to 0.2 mm long; bracteoles 2, 0.8–1.4 × 0.7–1.2 mm, subovate, attenuate, slightly pubescent mainly on the margins and central part. Male pedicel 2–3.7 mm long, glabrous. Male calyx 2–3-lobed; lobes 2.7–3 × 1.6–2.5 mm, ovate to lanceolate, cochleariform, apiculate, glabrous, sometimes with scattered hairs on margin. Petals 5, 2.9–3.7 × 2.5– 3.8 mm, ovate-elliptic, rounded to slightly acute, glabrous, white. Androphore 1.3–2 mm long, slightly bell-shaped, glabrous with simple, scattered hairs less than 0.1 mm long; androphore glands 5, 0.45–0.8 mm long, rectangular or square, unequal, sometimes emarginate, glabrous. Stamens 16–17(–20), 0.7–1.3(–1.8) mm long; filaments glabrous; anthers 0.3–0.6 × 0.3–0.5 mm, dorsifixed, extrorse; connective glabrous. Female inflorescence 7.9–15 × 4.4–9 cm; main axis pubescent; bracts 2.5–8.2 × 1.5 mm, the shorter ones narrowly lanceolate, and the longer ones foliaceous, oblanceolate, shortly petiolate, both attenuate, slightly pubescent; bracteoles 2, alternate to subopposite, 1.4–2 × 1–1.6 mm, broadly lanceolate, acute, slightly pubescent. Female pedicel 4.8–7 mm long, pubescent with scattered hairs. Female sepals 5, 1.9–2.8 × 1.5–1.8 mm, ovate, apex rounded, puberulous on the margin and with scattered hairs on the central part abaxially, imbricate. Petals 5, c. 3.8 × 2.8 mm, elliptic to broadly lanceolate, apex rounded, glabrous, colour unknown. Disc plane, irregularly thickened on the edge, glabrous. Ovary 3-locular, 2–3.3 mm diam., glabrous; styles 3, bifid, 1.3–1.7 mm long, glabrous, with stylar branches 0.9–1.4 mm long. Fruit capsular, 3-lobate, 6–6.4 mm long, ca. 9 mm diam., glabrous; pedicel 8–9.5 mm long, pubescent; cocci 4.5–6.3 mm wide; columella 4.6–5.6 mm long, persistent. Seeds ca. 4.3 × 3.8 mm, subglobose, ecarunculate, dark brown mottled with light brown.

Etymology:—The specific epithet refers to the exceptionally narrow leaves of this species.

Distribution and ecology:— Grossera angustifolia is so far known from a single locality in the Litoral province in Equatorial Guinea ( Fig. 3). It grows on rocky substrate along the Wele river, at 25 m elevation ( Fig. 2A ).

Additional specimen examined (paratype):— EQUATORIAL GUINEA. Litoral: carretera Bata-Sendje, km 40, bajo el puente sobre el río Wele (Benito), 25 m, 1º33’3”N, 9º49’43”E, 30 May 2014, F. Cabezas et al. 2116 (MA).

Discussion: — Grossera angustifolia falls into sect. Grossera which includes species with paniculate inflorescences and leaves with two glands at the junction of the petiole with the lamina. This section is composed of four additional species namely, Grossera paniculata Pax (1903: 281) , G. elongata Hutch. in Exell (1944: 294), G. major Pax (1903: 282) and G. multinervis Léonard (1955: 317) ( Barberá et al. 2014). Grossera angustifolia is characterised by narrowly elliptic leaves with short petiole, spirally arranged along branches ( Fig. 2B ). These leaf characteristics along with the riverine habitat suggest that G. angustifolia could be a rheophyte ( van Steenis 1981, 1987), able to resist the fast-flowing water during floods. Grossera angustifolia is most similar to G. paniculata , a widely distributed species in West Tropical Africa including Equatorial Guinea, however, the two species can be readily distinguished by leaf morphology, phyllotaxis, and petiole length. Other distinguishing features include the size of male and female inflorescences, sepals, male petals and fruits, and seed width ( Table 1).

Figures

FIGURE 1. Grossera angustifolia. A. Habit, male flowering branch. B. Glands at the junction of the petiole and lamina. C. Detail of leaf margin. D. Male flower. E. Male sepal. F. Male petal. G. Male flower without perianth (some stamens are not visible). H. Longitudinal section of male flower without perianth. I. Stamen, adaxial view. J. Stamen, abaxial view. K. Female flower without petals. L. Female sepal. M. Female petal. N. Female disc. O. Fruit. P. Columella. Q. Seed, ventral view. Drawn by J. Castillo based on Carvalho 4909.

FIGURE 2. A. Individuals of Grossera angustifolia growing along the Wele river. B. Detail of branch showing the spiral disposition of the leaves. C. Image of the holotype of G. angustifolia. D. Image of a representative specimen of G. paniculata. Photos in the field by M. Fero, images of herbarium sheets provided by the herbarium staff at MA.