Euphorbia cerralvensis Maya Lastra & V.W. Steinm., 2015

Maya-Lastra, Carlos A. & Steinmann, Victor W., 2015, Two new species of Euphorbia subg. Chamaesyce (Euphorbiaceae) from Baja California Sur, Mexico and their phylogenetic relationships, Phytotaxa 221 (3), pp. 265-278 : 271-272

Euphorbia cerralvensis Maya Lastra & V.W. Steinm. , sp. nov. ( Figs. 3 and 4 )

Similar to Euphorbia polycarpa but differs by having seeds with transverse ridges instead of being smooth, also it is phylogenetically related with E. dentosa , E. leucophylla , E. petrina , and E. brandegeei , species from which it is distinguished by its suffrutescent ascending habit.

Type:— MEXICO. Baja California Sur: Municipality of La Paz, Isla Cerralvo, Cañón de Los Viejitos, costado del Faro, 23°17′ N, 110°48′ W, 70 m, 8 October 1999, J. León de la Luz 9584 (holotype HCIB!).

Suffrutescent, 15–30 cm tall, highly branched, from a root up to 1 cm in diam.; stems ascending, 10–30 cm long, 0.3–3 mm diam., terete, sometimes in zigzag, glabrous, internodes 1–2.5 cm long. Leaves opposite; stipules interpetiolar, separate, subulate, 0.3–0.4 mm long, entire, glabrous or sometimes pubescent; petiole 0.7–1 mm long; lamina lanceolate to elliptic, 2–13 mm long, 0.7–3 mm wide, base slightly asymmetric, obtuse to cuneate, margin entire, apex acute to obtuse, glabrescent, slightly pubescent when young, midrib conspicuous beneath to the base, lateral veins inconspicuous. Cyathia solitary, terminal and axillary; peduncle 0.6–1.9 mm long, glabrate to pilose with whitish, linear, multicellular trichomes ca. 0.3 mm long, involucre campanulate, 0.8–1.2 mm long, 0.6–0.8 mm wide, pilose, with trichomes similar to those of the peduncle but sometimes with the intercellular walls pinkish; sinus U-shaped, 0.1–0.2 mm deep; lobes subulate to triangular, 0.2–0.3 mm long, fimbriate, with straight trichomes 0.1–0.2 mm long or sometimes glabrate, margin erose; glands transversally oblong, 0.1–0.2 mm long, 0.3–0.5 mm wide, reddish; appendages obovate or oblong, 0.8–1.3 mm long, 0.7–1.0 mm wide, white, margin undulate, sometimes with 2–3 undulations 0.1 mm deep; bracteoles few, terete, plumose at apex. Staminate flowers 20–30. Ovary 3-lobed, glabrous, sometimes with a few trichomes; styles 3, bifid to middle, slightly thickened apically, cylindrical, glabrous, 0.2–0.3 mm long. Capsule with a pedicel 0.5–0.7 mm long; ovoid-globose, 1.2–1.5 mm long, 1.2–1.6 mm wide, green, keels reddish, angular to slightly rounded, pilose with some straight trichomes, sometimes curved; gynophore exserted ca. 0.7 mm long, pilose apically; columella ca. 1.6 mm long. Seeds narrowly ovoid, transversely quadrangular, ca. 1.2 mm long, ca. 0.7 mm wide, base truncate, apex acute, angles slightly pronounced, dorsal facets flat, coat with transversal whitish ridges that do not cross the dorsal keel, reddish-brown, ecarunculate.

Distribution and habitat:— This is a narrowly endemic species currently known only from the Isla Cerralvo (also known as Isla Jacques Cousteau), Baja California Sur, in the Gulf of California. Collections have been made from both the northern and southern portions of the island and at elevations of 10 to 300 m. It is apparently common on this uninhabited island.

Etymology:— Because this species has been found only on Isla Cerralvo, we consider it important to recognize the floristic importance of the region with the name of this new species.

Morphology and phylogenetic relationships:— Euphorbia cerralvensis is very different from other Euphorbia species in the region. Although the collections were identified as Euphorbia polycarpa , it is readily distinguished by its transversally ridged seeds. In contrast, the seeds of Euphorbia polycarpa are smooth. It is distantly related to E. polycarpa in both phylogenetic reconstructions ( Figs. 1 , 2 ) and it belongs to a clade with E. dentosa , E. leucophylla , E. petrina , and E. brandegeei . Euphorbia cerralvensis differs from all these species by its suffrutescent ascending habit; the others are herbaceous and prostrate. Furthermore, it can be distinguished from E. dentosa and E. leucophylla by the entire margin of the leaf blades, because in these other species the margin is dentate or serrulate. By the absence of pubescence in the herbage it can be separated from E. petrina . Finally the woody stem permits distinguishing this species from E. brandegeei .

Other collections examined (paratypes):— MEXICO. Baja California Sur: Municipality of La Paz, central west side of the Cerralvo Island, 24°13′ N, 109°53′ W, 300 m, 7 October 1994, J. Navarro 138 (HCIB!), Cerralvo Island, 24°15′ N, 109°52′ W, 150 m, 26 November 1994, M. Dominguez 923 (HCIB!) Arroyo, 24°19′ N, 109°56′ W, 10 m, 29 September 1996, J. León de la Luz 7989 (HCIB!), South end of Cerralvo Island, 24°09′ N, 109°50′ W, 3 April 1952, R. Moran 3588 (CAS!), Ruffo Ranch Canyon, Cerralvo Island, 24°11′ N, 109°51′ W, 200 m, 16 April 1962, R. Moran 9526 (SD!).

Figures

FIGURE 1. Phylogenetic reconstruction using the majority rule consensus from Bayesian analyses of the chloroplast region psbA-trnH. Numbers above the branches are Bayesian posterior probabilities (PP). The new species are marked in bold. “Exvarieties” of Euphorbia polycarpa are marked with an asterisk.

FIGURE 2. Phylogenetic reconstruction using the majority rule consensus from Bayesian analyses of the nuclear region ITS. Numbers above the branches are Bayesian posterior probabilities (PP). The new species are marked in bold. “Exvarieties” of Euphorbia polycarpa are marked with an asterisk.

FIGURE 3. Distribution map of the new species of Euphorbia in Baja California Sur (Mexico). A. Detail of Cerralvo Island.

FIGURE 4. Euphorbia cerralvensis Maya Lastra & V.W. Steinm. A. Detail of involucral lobes; B. seed (basal view) C. seed (1. ventral and 2. dorsal view); D. mature cyathium; E. immature cyathium; F. capsule; G. habit; H. detail of a flowering branch. Based on J. León de la Luz 9584 (HCIB).