Sedum pyriseminum E. Pérez-Calix, 2016

Pérez-Calix, Emmanuel, 2016, Sedum pyriseminum (Crassulaceae), a morphologically remarkable new annual species from the state of Durango, Mexico, Phytotaxa 255 (3), pp. 297-300 : 298-300

Sedum pyriseminum E. Pérez-Calix , spec. nov., Fig. 1 .

Sedum pyriseminum differs from Sedum vinicolor by the elliptic to oblong-elliptic or obovate leaves, the sepals of unequal sizes, the white short gamopetalous corolla, the fungiform yellow nectaria, and the pyriform, smooth, brownish seeds.

TYPE:— MEXICO. Durango: municipality Pueblo Nuevo, Mexiquillo , 2550 m, 23°43’9.20”N ; 105°40’9.95”O, 19 September 2013, E. Pérez 5268 (holotype: IEB!; isotypes: CIIDIR!, MEXU!) .

Herbaceous annual plants, lithophytic, 1.5–2 cm high, succulent, glabrous. Roots fibrous, branching from a short, slightly thickened main root. Stem branched at the middle, ca 1 mm diameter, partly rugulose at the surface, reddish. Leaves sessile, broadly elliptic to oblong-elliptic or obovate, 3.8–5 mm long, 2–3.8 mm broad, ca 2 mm thick, semicircular in transversal section, apex obtuse and thickened, truncate, spurred at the base, abaxially flattened, adaxially convex, green towards reddish-brown. Inflorescence terminal, cymose, with 1–8 cincinniform branches, with up to 8 or less crowded flowers. Flowers sessile or with pedicels to 1 mm long. Sepals 5, clearly of different sizes, free; the longest sepal oblong, lanceolate or ovate-oblong, 2–3.5(–4.5) x 1–1.5(–2.5) mm, apex rounded, thickened; the shortest one lanceolate, 1–1.5(–2.5) x 0.3– 0.6(–0.8) mm. Corolla white, short gamopetalous; the limb ca 2 mm diameter, the tube 0.5–1 mm long; petals 5, ovate to ovate-lanceolate, 2–3 mm long, apex acute, internally sulcate, keeled externally, apex cucullate. Stamens 10, arranged in two alternating whorls, the outer one opposite the petals, basally fused and inserted in the corolla tube, filaments ca 1.5 mm long, clearly flattened and broadening towards the base, anthers black, ca 0.5 mm long. Nectaries fungiform, yellow, with a stalk ca 1 mm long. Ovary globose, carpels 5, fused ca 0.5 mm at the base style ca 0.5 mm, stigma inconspicuous; ovules 8 per carpel, pyriform. Follicles ca 2 mm long, slightly extended in the apex, reddish. Seeds 6–8 per follicle, pyriform, ca 0.7 mm long, smooth, brownish.

Distribution, habitat, phenology:— Sedum pyriseminum is only known from the type locality, “Jardín de Piedras”, in Mexiquillo, municipality of Pueblo Nuevo, Durango, Mexico. It grows on flat terrain on bare rock, especially in fissures filled with sand and gravel in which runoffs are formed during the rainy season. The species has been registered as flowering and fruiting in September.

Observations:—The new taxon superficially resembles Sedum vinicolor S. Watson (1886: 428) (= Sedum forreri E. L. Greene (1888: 162)) . Table 1 shows the characters by which both species can be distinguished from each other. Due to its peculiar and unique features, such as as the filaments which are flattened and broadened towards the base and shortly fused to a ring-like structure at the very base; the fungiform nectaries with a relatively long stalk; as well as the thick and pyriform seeds without any surface patterning, which can be observed with a stereoscopic microscope with magnification 45×, this new species is morphologically one of the most aberrant species in Sedum and apparently without close relatives.

Conservation status:— Sedum pyriseminum is here assessed as Vulnerable according to Criterion D subcriteria 1 and 2 (VU D1 + 2) ( IUCN (2012). The single known population is estimated to consist of less than 1000 mature individuals and its area of occupancy is very limited (≤ 200 m 2). Morever, the locality of Mexiquillo is used for recreational activities, as a consequence of which people walk and drive over the type locality. This exposes populations of Sedum pyriseminum to trampling and movement of the sand where they grow.

Etymology:—The specific epithet refers to the pear-shaped seed, which is rare in the genus Sedum . Paratypes:— MEXICO. Durango: municipality Pueblo Nuevo, Mexiquillo, 2550 m, 23°43’9.20”N; 105°40’9.95”O,

19 September 2006, E. Pérez 4710 ( IEB!, CIIDIR!, MEXU!) ; ibid .; 27 September 2005, S. Zamudio 13228 ( IEB!) .

Figures

FIGURE 1. Sedum pyriseminum E. Pérez-Calix, spec. nov. A) Habit; B) Detail of the plant showing the leaf insertion; C) Lateral view of flower; D) Lateral view of corolla; E) Superior view of flower; F) Dorsal view of nectary; G) Superior view of nectary; H) Follicles; I) Seed. Illustration by Alfonso Barbosa based on the holotype (E. Pérez 5268 (IEB)).