Euphorbia riinae V.W. Steinm., 2013

Steinmann, Victor W., 2013, Three new species of Euphorbia subg. Chamaesyce (Euphorbiaceae) from Bolivia, Phytotaxa 114 (1), pp. 23-32 : 28-30

Euphorbia riinae V.W. Steinm. , sp. nov. ( Fig. 3 )

Similar to Euphorbia gymnoclada but differs by possessing wider involucral glands that are not concealed by the appendages and longer styles that exceed the ovary in length.

Type:— BOLIVIA. Santa Cruz: Prov. Velasco, Parque Nacional Noel Kempff Mercado, Serrania de Caparuch , senda de GEOBOL, encima de la meseta, aprox. 15 km al SE de Los Fierros, 700 m, 14°33'30"S, 60°45'41"W, 23 November 1994 (fl, fr), T . J . Killeen & O . Peña 7176 (holotype MO!, isotypes DAV!, USZ) .

Perennial herb from a thickened, rhizomatous rootstock. Stems erect to ascending, numerous and congested, dried bases of stems from previous season also present at the apex of the rootstock, unbranched or up to 2× dichotomously branched, 14–40 cm tall, green and photosynthetic, wiry, glabrous, longitudinally striate (at least upon drying), terete, internodes 3–11 cm long. Leaves opposite, caducous; stipules at the base of the blade, inconspicuous, glanduliform, conical, 0.1–0.2 mm, glabrous; petiole lacking; blade linear to narrowly elliptic when young, becoming elliptic to obovate, 2.8–3.9 × 0.8–1.9 mm, margin entire or slightly undulate, hyaline, apex acute, base attenuate, only the mid-vein conspicuous, glabrous or the adaxial side puberulent at the base with hairs 0.1–0.3 mm long. Cyathia solitary in the upper nodes or terminating the stems; peduncle 0.8–4.1 mm long, glabrous. Involucre broadly obconical, 2.7–3.1 × 2.1–3.4 mm; glands 5 per involucre, transversly oblong to slightly reniform, 0.4–0.5 × 1.1–1.4 mm; appendages present, equal, divided into 3 or 4(–5) subulate to triangular divisions, 0.9–1.6 × 1.6–2.8 mm, not concealing the glands, white to yellowish; lobes ovate to transversely oblong, 0.6–0.9 × 0.9–1.1 mm, erose with very short hairs. Staminate flowers 20– 25, bracteoles few, filiform, pilose. Ovary globose, 3-lobed, glabrous; styles 3, filiform, longer than the ovary, united in the lower 1/2, undivided, 2.2–3.5 mm long, glabrous, terete, tapering at the apex. Capsule on an exserted gynophore 2.5–4.0 mm long, oblate, strongly 3-lobed, 3.2–3.9 × 3.8–4.5 mm; columella 2.9–3.8 mm. Seeds ovoid, rounded in cross-section but with a prominent dorsal keel, 3.2–3.6 × 2.2–2.3 mm, base rounded, apex pointed, foveolate with shallow, irregular, spreading depressions, mottled light-dark brown, ecarunculate.

Distribution, habitat and phenology:— Euphorbia riinae is known from the Huanchaca Plateau, Parque Nacional Noel Kempff Mercado, in the province of Velasco, department of Santa Cruz. A detailed description of this area and its biota can be found in Killen & Schulenberg (1998). The new species occurs in sandy soils of tropical savannas at elevations of approximately 700 m, and it prospers in response to periodic fires that occur at the end of the dry season. Flowering individuals have been found in October and November, with mature fruits present at the end of November.

Etymology:—It is a pleasure to name this species in honor of Dr. Ricarda Riina. She is a primary participant in the Euphorbia Planetary Biodiversity Inventory Project , a global initiative to document, describe and investigate all known species of Euphorbia , and has made significant advances to our understanding of the genus Euphorbia , and in particular Euphorbia sect. Crossadenia Boissier (1862: 64) .

Additional specimens (paratypes) examined:— BOLIVIA. Santa Cruz: Prov. Velasco, Parque Nacional Noel Kempff Mercado, Los Fierros ( Serranía Caparuch ), 30 October 1994 (fl), B . Mostacedo et al. 2431 ( NY!, USZ); Prov. Velasco, Meseta de Caparuch , en el camino a la Meseta desde los Fierros, 14°30.23'S, 60°44.97'W, 710 m, 14 November 2003 (fl), J . R .I. Wood, D. Goyder , W . Biggs & M . Mercado 19951 ( K!); Prov. Velasco, Parque Nacional Noel Kempff Mercado, Serranía de Huanchaca , cerca del campamento Huanchaca 2, zona de la piscina, 14.3014°S, 60.4458°W, 707 m, 03 November 2003 (fl), J . R .I. Wood, D. Villaroel, D. Soto & P . Pozo 25214 ( K!, USZ) .

Discussion:—The new species belongs to Euphorbia subg. Chamaesyce sect. Crossadenia , a small taxon of ten perennial herbs otherwise restricted to eastern-central Brazil ( Carneiro-Torres et al. 2012). This assemblage was previously treated within subg. Agaloma (e.g., by Wheeler 1943), but phylogenetic analyses have demonstrated that subg. Agaloma is polyphyletic. Although difficult to characterize on the basis of morphological features, sect. Crossadenia forms a strongly supported monophyletic group in recent phylogenetic studies (e.g., Steinmann & Porter 2002, Yang et al. 2012). The possession of digitately divided involucral appendages warrant placement of E. riinae in subsect. Ephedropeplus ( Müller 1874: 668) Pax (1891: 106) 1, where it is most-similar and without doubt closely related to Euphorbia gymnoclada Boissier (1860: 20) . The two species share many traits including an herbaceous, nearly leafless habit; green photosynthetic stems; diminutive, caducous opposite leaves that are sometime puberulent towards the adaxial base and subtended by minute glanduliform stipules; 5 involucral glands; 3–5-parted involucral appendages; and entire styles that are united into a column proximally. Photos of E. gymnoclada were provided by Carneiro-Torres et al. (2012: figs. 2F–H). It is worth noting that the Huanchaca Plateau is composed of sandstone, and both E. gymnoclada and E. riinae also share a preference for sandy soils. In addition to their widely separated distributions, the two species differ as follows:

1. Glands 0.3–0.9 mm wide, concealed by the arching involucral appendages; styles 1.2–1.4 mm long, shorter than the ovary ........................................................................................................................................ Euphorbia gymnoclada

- Glands 1.1–1.4 mm wide, exposed; styles 2.2–3.1 mm long, longer than the ovary ........................ Euphorbia riinae

1 Riina recently proposed subsect. Sarcodes Riina (in Yang et al. 2012: 780) for a clade that contains six Brazilian species, including E. gymnoclada . However, subsect. Ephedropeplus, the type of which is E. gymnoclada , is the oldest available name for the group at this rank and has more than a century priority over subsect. Sarcodes .

Figures

FIGURE 3. Euphorbia riinae. A) Habit; B) Young vegetative shoot; C) Leaves; D) Cyathium subtended by two cyathophylls; E) Involucre gland with 3-parted appendage, and involucral lobes; F) Staminate flower and subtending androphore; G) Seed, ventral (right) and dorsal (left) views. Based on Killeen & Peña 7176 (MO), and drawn by José Manuel Ramírez-Amezcua.