Dasylirion micropterum Villarreal, A.E. Estrada & Encina, 2016

Villarreal-Quintanilla, José A., Estrada-Castillón, Eduardo, Valdés, M. Humberto Reyes-, Encina-Domínguez, Juan A., Martínez, Octavio & Godinez, Fernando Hernández-, 2016, Dasylirion micropterum (Asparagaceae), a new species from Sierra Madre Oriental, Mexico, Phytotaxa 253 (2), pp. 139-146 : 141-144

Dasylirion micropterum Villarreal, A.E. Estrada & Encina sp. nov. ( Figs. 1–2 ).

Similar to Dasylirion miquihuanense Bogler , but with erect flat leaves; inflorescence nearly as long as the peduncle, with 3(–5) side branches; fruit 3–4 mm long, 2.5–3.0 mm wide, fruit lateral wings 0.4–0.6 mm wide, the notch shallow 0.2–0.3 mm deep; distribution in the Sierra Madre Oriental.

Type: — MÉXICO. Coahuila: Municipio de Arteaga, Ejido Nuncio, Sierra La Veleta, ladera con exposición sur, 25º12´52.78´´N, 100º16´47.57´´W, 2843 m de elevación, 29 September 2014 (fr.), matorral rosetófilo de Dasylirion con Quercus striatula y Arctostaphylos pungens , plantas aisladas de Quercus pringlei y Agave gentryi . J. A. Encina 4177, Z. A. Zamora & I. Moran (holotype MEXU; isotypes ANSM, CFNL, ENCB, TEX).

Perennial single plants, with short trunks usually less than 40 cm high; rosette crowns openly spreading, 120–200 cm wide, 80–140 cm high. Leaves 60–120 per plant, linear, 70–100 × 1.6–2.4 cm, ascending, the lower reflexed, dark green and becoming green-yellowish when mature, the base enlarged, spoon shaped, the apex entire, acute, usually curved, the margins straight, prickles 54–60 pairs, antrorse, 6–12 mm apart, yellow, with papillose upper surface. Flowering stalk 1.8–2.4 m tall, the inflorescence a racemose panicle, congested, largely oblong, 130–190 × 10–15 cm, purple to tawny; bracts long triangular, 20–28 cm long, 5–6 cm wide at the base, chartaceous, the margins entire, the apex with a short and weak spine. Staminate fascicles with a short central axis 4–9 mm long, racemes 3–5, 3–6 cm long, ascending, bracts lanceolate, 3–5 cm long; staminate flowers with floral bracts, 2–2.5 mm long, laciniate, pedicels 1–2 mm long, tepals obovate, 2.0– 2.5 mm long, denticulate. Pistilate fascicles with no central axis, racemes 3(–5), (5–) 7–12 cm long, usually the central longer, ascending, bracts lanceolate, 3–6 cm long, 4–6 mm wide; pistilate flowers with floral bracts 1.0– 1.5 mm long, attenuate, pedicels 0.5–0.8 mm long, elongating in fruit to 1.5–2.0 mm, tepals oblong, 1.5–2.0 mm long, entire, shortly apiculate; ovary 3-angled, style 0.2–0.3 mm long, stigma lobes 0.1–0.2 mm long. Fruit ovate-oblong, 3–4 mm long, 2.5–3.0 mm wide; wings of lateral side 0.4–0.6 mm wide, apical side 0.6–1.1 mm, notch shallow 0.2–0.3 mm deep, style and stigma 0.4–0.6 mm, slightly exerted; seed trigonous with rounded edges, 2.5–2.8 mm × 2.3–2.6 mm, brown-yellowish.

Distribution, habitat and phenology: —The species occurs in dense populations in southeastern Coahuila state, mostly on south-facing slopes, in limestone soils, from 2700 to 2850 m of elevation. The area is dominated by a dwarf oak community consisting mainly of Quercus striatula Trelease (1924: 93) , Q. pringlei Seemen ex Loesener (1900: 96) , Arctostaphylos pungens Kunth (1818: 278) , Ceanothus buxifolius Willd. ex Kunth (1824: 62) , Agave gentryi Ullrich (1990: 211) , and occasional Pinus hartwegii Lindley (1839: 62) and Pseudotsuga menziesii ( Mirbel 1825: 63) Franco (1950: 74) ( Figure 3 ). Flowering time ranges from May to August, and fruiting occurs from August to November.

Eponimy: —The specific epithet refers to the very short fruit wings.

Common name: —Sotol.

Additional specimens examined: — Type locality, 13 July 2014, J.A. Encina 3830, Z.A. Zamora & A. García (ANSM!, MEXU!).

Discussion: —Morphologically, Dasylirion micropterum is similar to D. miquihuanense from southern Nuevo León and Tamaulipas. Both species have ascending, dark green leaves, fruits less than 7 mm long and fruit wings less than 2 mm wide. However, D. micropterum differs by having flat and papillose leaves, a longer inflorescence, less side branches of the inflorescence and smaller fruit, with much narrower fruit wings ( Table 1). Additionally, D. micropterum is a plant having a trunk no more than 40 cm tall and occurs in the Sierra Madre Oriental in Coahuila and probably Nuevo Leon border in temperate areas with submontane scrub at 2700–2850 m of elevation. In contrast, D. miquihuanense has a trunk up to 200 cm tall and is found in dry hills and low mountains with desert scrub in southern Nuevo Leon and southwestern Tamaulipas at 1700–1900 m of elevation. Dasylirion berlandieri also occurs within the Sierra Madre Oriental, but has the leaves usually arching downwards and larger and wider fruits with a deeper notch and the style clearly exerted. D. berlandieri occurs on the eastern side of the Sierra Madre Oriental and in other mountains on the Planicie Costera (Nuevo Leon, Tamaulipas and San Luis Potosi), within the pine-oak forest, while D. micropterum is located on the western side of the Sierra Madre Oriental, with submontane oak scrub.

All rbcL and matK samples studied for both D. micropterum and D. miquihuanense were identical within species. Therefore, a single sequence was submitted to the GenBank for each species and region studied. GenBank accession numbers are as follow: D. micropterum , rbcl, KU535885; D. miquihuanense , rbcl, KU535886; D. micropterum , matK, KU535883; D. miquihuanense , matK, KU535884.

Regarding the rbcL plastidial region, all sequences for both D. micropterum and D. miquihuanense were identical among species, and did not show any specific variation. However, some nucleotide variations were found for matK and are reported in Table 3. Two nucleotide substitutions were found between D. micropterum and D. miquihuanense , which corresponds to the number of substitutions found between D. serratifolium and D. wheeleri , and between D. serratifolium and D. miquihuanense . Furthermore, the two substituted sites in D. micropterum , corresponding to the bases 608 and 649 of the complete matK gen sequence, are unique in this species, with regards to the three reference taxa.

At the phylogenetic approach, the dendrograms show in general D. miquihuanense as the closest related species to D. micropterum , whereas D. wheeleri and D. serratifolium form a single group ( Figure 4 ). The largest distance within the genus occurs between D. micropterum and D. wheeleri .

Figures

FIGURE 1. Dasylirion micropterum. A. A population. B. Flowering plants. C. Portion of the pistilate inflorescence. D. Fruits close up. Photos by J. A. Encina.

FIGURE 2. Dasylirion micropterum.A. Leaf. B. Bract. C. Staminate flower. D. Pistilate flower. E. Fruit. F. Seed. Illustrated by G. Gloria Bazaldúa.

FIGURE 3. Distribution of three species of Dasylirion.

FIGURE 4. Phylogenetic trees for Dasylirion micropterum, three reference species of the same genus, and Nolina atopocarpa as an outgroup species. It is based on the matK sequence with four models: NJ = Neighbor-Joining (Log likelihood = -2289.811), MP = Maximum Parsimony (Log likelihood = -8329.362), UPGMA = Unweighted Pair Group Method with Arithmetic Mean (Log likelihood = -2287.411), ML = Maximum Likelihood (Log likelihood = -2283.342). The node labels are bootstrap values.