Cascabela balsaensis L.O. Alvarado and J.C. Soto, 2014

Alvarado-Cárdenas, Leonardo O. & Núñez, José Carmen Soto, 2014, A new species of Cascabela (Apocynaceae; Rauvolfioideae, Plumerieae) from Michoacán, Mexico, Phytotaxa 177 (3), pp. 163-170 : 164-169

Cascabela balsaensis L.O. Alvarado and J.C. Soto , sp. nov. ( Fig. 1 , 2 )

Cascabela balsaensis resembles to Cascabela thevetioides and Cascabela pinifolia , but is easily recognized by the leaves ellipticlanceolate to lanceolate, densely pubescent on both sides, and with conspicuous venation. The inflorescence is a simple corymb with smaller flowers, and calycine colleters are small and distributed in a row or irregularly.

Type:— MEXICO. Michoacán: Municipio de Huetamo de Núñez. En la subida al Cerro Dolores, aprox 4.5 km al NE de La Parota y a 10.5 km al NE de Huetamo , por la brecha a La Estancia, 600 m, 18°40’0.61”N, - 100°51’56.95”W, 22 June 2009, Soto 15792 (holotype MEXU! isotypes FCME!, MO!) .

Tree or shrub with smooth woody stems, 2.5–5 m tall, green, young branches sparsely pubescent. Leaves alternate with colleters present in the leaf axils, in groups of 10–18, 1– 3 mm long, conic to subulate; petioles 1–3 mm long, pubescent; lamina 5.5–12 × 0.4–1.1 cm, elliptic-lanceolate to lanceolate, base and apex acute, firmly membranaceous to subcoriaceous, secondary venation conspicuous, 34–46 pairs of veins, densely pubescent abaxially and adaxially. Cymose Inflorescences, corymb type, 8–12 cm long, 4–6–flowered; peduncles 3–5(13) mm long, pubescent. Bracts 3–8 mm long, ovate-lanceolate to oblong-lanceolate, foliaceous, pubescent on both surfaces, with colleters at the base adaxially. Pedicels 17–38 mm long, pubescent. Calyx of five sepals connate at the base; sepals (4) 6–11 mm long, subequal, ovate-lanceolate to oblong-ovate, foliaceous, 10–nerved, pubescent on both surfaces, with (0–)4–6 small colleters, ca. 0.5 mm long, at the base adaxially, in a row or sometimes irregularly distributed. Corolla 45–52 mm long, infundibuliform, yellow; lower tube 8–12 × 3.5–6 mm, glabrous externally, with retrorse hairs internally, upper tube 8– 15 × 15–18 mm, campanulate, glabrous on both surfaces, lobes 23–26 × (13) 18–20 mm long, obliquely oblong-ovate, spreading, sparsely puberulent, margin ciliate. Stamens subsessile; anthers 5–6 mm long, ovate, apically acuminate, dehiscence latrorse; suprastaminal appendages densely tomentose, infrastaminal appendages glabrous. Pistil 14–16 mm long, glabrous; ovary 3–3.5 mm long, glabrous; style head 3–3.5 mm long, umbraculiform, with two massive conical, papillose tips, and a ten lobed basal collar; nectary disc 2–3 mm high, fused into a ring, lobed at the apex. Drupe 35–40 × 35–45 mm, subglobose, glabrous, black, endocarp stony, irregularly deltoid, not lenticellate. Seed adherent to lignified placenta, oblong, 11–14 × 10 mm, white to yellowish, with a marginal fimbriate wing.

Habitat:— Cascabela balsaensis grows in dry tropical forest, associated with members of Bursera Jacq. ex L. (1762:471), Anacardiaceae , such as Pseudosmodingium perniciosum (Kunth) Engler (1881: 420) and Cyrtocarpa procera Kunth (1824: 20) , and Fabaceae , such as Lysiloma divaricatum (Jacq.) J.F. Macbride (1919: 6) and Haematoxylum brasiletto H. Karsten (1862: 27) , etc. ( Fig. 3 ), on rocky limestone hills, at an elevation of 400–800 m in the western region of Balsas Basin with mean annual precipitation of 978 mm and temperatures between 24–35° C ( Fernández et al. 1998).

Distribution:—The new species of Cascabela apparently is known only from the municipality of Huetamo, Michoacán, Mexico ( Fig. 3 ). It grows in the Balsas Basin, an area highlighted as rich in endemism ( Rzedowski 1991, Fernández et al. 1998), particularly in the western portion known as the Lower Balsas. Interestingly, this new species shares a similar range to that other endemic Apocynaceae , such as C. pinifolia and Fernaldia asperoglottis Woodson (1939: 96) . In addition, C. balsaensis grows simpatrically with C. pinifolia at the Huetamo locality, but it was not noticed in previous botanical surveys because of its resemblance to C. pinifolia and C. thevetioides .

Etymology:—The specific epithet refers to the region of the Balsas Basin where the new species occurs, which is an important phytogeographic area, regarded as a center of species diversity and endemism in several groups such as Burseraceae , Cactaceae , Euphorbiaceae , Fabaceae , etc. ( Sousa & Soto 1987, Rzedowski 1991, Fernández et al. 1998).

Phenology:—Flowering March to June, fruiting March to September.

Common names and uses:—The local name of this species is “camé” or “camín”, which are names used to refer other species of Cascabela . This species is sometimes used as an ornamental, cultivated in yards around houses. The people of the community mentioned that they sometimes eat the mature fruits.

Conservation status:—The new species is only known from the type locality at Huetamo ( Fig. 3 ). At this locality, Cascabela balsaensis is sometimes used as a living fence, as is also the case for C. pinifolia , and seems to tolerate some degree of disturbance. Considering that the new species is found only in a small area of Michoacán State and that grazing may significantly reduce the number of individuals in the future, it is suggested to add C. balsaensis to the category of Vulnerable (VU B2, C), based on the IUCN criteria ( IUCN 2013).

Taxonomic remarks:—The last valid taxon described for the genus was C. pinifolia (described as Thevetia peruviana var. pinifolia Standl. & Steyerm. in Leavenworth 1946: 185), more than 60 years ago. This new species of Cascabela represents a noteworthy contribution to the diversity of the genus, and increases the number of species of the genus endemic to Mexico to three (together with C. pinifolia and C. thevetiodes ). This species seems closely related to C. pinifolia and C. thevetiodes , based on similarities in leaf attributes and flower size ( Fig. 4 , 5 ). Cascabela balsaensis and C. pinifolia have pubescent peduncles and sepals, and similar flower sizes ( Figs. 4 B, D ), but the former differs mainly by its firmly membranaceous to subcoriacous leaves (vs. membranaceous), conspicuous secondary venation (vs. inconspicuous), elliptic-lanceolate to lanceolate leaves (vs. linear to filiform leaves), leaves wider (4) 6–11 mm (vs. 1–3 mm), and densely pubescent on both surfaces (vs. glabrous to sparsely puberulent). With C. thevetiodes , the new species shares a similar leaf shape and conspicuous secondary venation ( Figs. 5 A–B, G–H ), but differs by the dense pubescence on both sides of the leaves (vs. glabrous adaxially and sparsely tomentose abaxially), inflorescences that are simple corymb (vs. duplicate or compound corymb), and flowers (vs. 72–95 mm). The new species shares some similarities with C. ovata in the conspicuous secondary venation, pubescence, and subcoriaceous leaves ( Figs. 4 A, C ; 5 A–B, E–F ). However, C. balsaensis has elliptic-lanceolate to lanceolate leaves (vs. spatulate to obovate) and smaller flowers. In addition, C. balsaensis has small calycine colleters, in a row or sometimes of irregular distribution, which contrast with the other species with numerous and larger colleters distributed in a row.

Additional specimens examined (paratypes): MEXICO. Michoacán: Municipio de Huetamo de Núñez. En Huetamo , en el barrio de Las Colonias. Cultivated, 400 m, 3 September 1982, Soto 4274 ( MEXU) . En la subida al Cerro Dolores, aprox 4.5 km al NE de La Parota y a 10.5 km al NE de Huetamo , por la brecha a La Estancia, 600 m, 18°40’0.61”N, - 100°51’56.95”W, 22 June 2009, Soto 15792 ( MEXU) .

Figures

FIGURE 1. Holotype of Cascabela balsaensis.

FIGURE 2. Cascabela balsaensis. A. Habit (Scale bar 1 m). B. Branch with leaves and fruit (Scale bar 10 cm). C. Leaves (Scale bar 10 cm). D. Fruit (Scale bar 5 cm).

FIGURE 3. Map of known distribution of Cascabela balsaensis (star).

FIGURE 4. Comparison of flower sizes between Cascabela balsaensis (A), C. pinifolia (B), C. ovata (C), and C. thevetioides (D).

FIGURE 5. Comparison of leaf pubescence between Cascabela balsaensis (A, B), C. pinifolia (C, D), C. ovata (E, F), and C. thevetioides (G, H), scale bar 2 mm.