Euphorbia beckii V.W. Steinm., 2013

Steinmann, Victor W., 2013, Three new species of Euphorbia subg. Chamaesyce (Euphorbiaceae) from Bolivia, Phytotaxa 114 (1), pp. 23-32 : 24-26

Euphorbia beckii V.W. Steinm. , sp. nov. ( Fig. 1 )

Similar to Euphorbia viridis but differing by alternate lower leaves and seeds possessing a prominent, persistent caruncle and lacking tubercules.

Type:— BOLIVIA. La Paz: Prov. Bautista Saavedra, A . N. M . I. Apolobamba, Río Charazani , orilla sur, 1750 m, 15°12'56"S, 68°48'12"W, 18 April 2005 (fl, fr), A . Fuentes , R . Cuevas , E . Cuevas & H . Pariamo 6928 (holotype MO!) .

Perennial herb from a thickened, elongated tuber. Stems erect to ascending, few arising from the base, little branched, with a few bifurcations towards the tips, to 50 cm tall, stems glabrous or sparsely villous, hairs irregularly bent and 0.5–0.8 mm long, terete, faintly longitudinally striate (at least upon drying), with prominent protuberances when the leaves fall, internodes 0.9–3.8 cm long. Leaves alternate below, opposite in the inflorescences; stipules at the bases of the petiole, inconspicuous, glanduliform, conical to deltoid, 0.2–0.3 mm, glabrous; petiole slender, 1.1–2.4 cm long, villous; blade ovate to rarely elliptic, 2.2–3.6 × 1.3–2.4 cm, membranaceous, margin entire, apex obtuse, base rounded to broadly cuneate, pinnate with 7–9 pairs of lateral veins, both surfaces sericeous, but the lower more densely so. Cyathia in weakly defined terminal cymes, 7–9 mm long, subtended by opposite cyathophylls similar to the stem leaves; peduncle 3.3–4.2 mm long, glabrous. Involucre campanulate, 1.7–1.9 × 2.2–2.6 mm, outer surface sericeous or villous towards the rim, inner surface puberulent towards the rim; glands 4(–5) per involucre, transversely elliptic-oblong, 0.5– 0.7 × 0.8–1.6 mm, slightly plicate; appendages present, equal, transversely oblong-elliptic, 0.9–1.3 × 1.8–2.1 mm, margin irregularly crenulate, surface sericeous or villous, greenish; lobes oblong to nearly rectangular, 0.4–0.5 mm long, pilose, apex fimbriate. Staminate flowers 25–30; bracteoles numerous, filiform, densely pilose. Ovary globose, sericeous or villous; styles 3, free to the base, bifid 1/4 to 1/2 their length, 0.9–1.4 mm long, glabrous, terete, slightly flattened at the apex. Capsule on a glabrous, exserted gynophore 2.7–4.3 mm long, not seen at maturity (all of the cocci present on the specimen have already dehisced), approximately 3.8– 4.0 mm long, sericeous or villous; columella 3.5–3.8 mm long. Seeds obloid, rounded in cross-section, 2.7– 2.8 × 2.0– 2.2 mm, base and apex rounded, foveolate with small, shallow, circular depressions, brown, and with transverse ridges that pass through the dorsal keel, tan, caruncule present, hood-like, 0.6 × 0.9–1.0 mm, cream-yellow.

Distribution, habitat and phenology:— Euphorbia beckii is known from a single specimen gathered at an elevation of 1750 m in the Área Natural de Manejo Integrado of Apolobamba, province of Bautista Saavedra, department of La Paz, where it grows among rocks in tropical deciduous forest. Flowering and fruiting occur simultaneously and have been recorded in April, but likely also occur in other months.

Etymology:—The specific epithet is in reverence to Dr. Stephan G. Beck, renowned ecologist, botanist, and director of the Herbario Nacional de Bolivia (LPB), whose decades of research on Bolivian plants have greatly enhanced our knowledge of the flora of this biologically diverse country.

Discussion:—Based on the possession of prominent involucral appendages together with leaves having long, slender petioles and inconspicuous, glandular stipules, Euphorbia beckii belongs to Euphorbia subg. Chamaesyce sect. Alectoroctonum Baillon (1858: 284) . This assemblage was previously treated as part of the paraphyletic Euphorbia subg. Agaloma ( Rafinesque 1836 [1838]: 116) House (1924: 471), e.g., by Wheeler (1943). The new species resembles most closely Euphorbia viridis (Klotzsch & Garcke in Klotzsch 1860: 39) Boissier (1862: 62), a frequent component of tropical forests distributed from Ecuador to Bolivia, and the cyathia of the two species are nearly identical. However, E. beckii differs by having alternate (vs. opposite or verticillate) leaves. Furthermore, the seeds of the new taxon lack tubercules and possess a prominent (0.9–1.0 mm wide), persistent caruncle. In contrast, the seeds of E. viridis are tuberculate and either ecarunculate or with a minute (<0.4 mm wide), caducous caruncle.

Figures

FIGURE 1. Euphorbia beckii. A) Habit; B) Detail of stipule; C) Flowering branchlet; D) Cyathium after fruit dehiscence; E) Involucral gland, appendage and lobes; F) Dehisced coccus; G) Seed, ventral (left) and dorsal (right) views. Based on Fuentes et al. 6928 (MO), and drawn by José Manuel Ramírez-Amezcua.