A new species, Lepidonia alba (Asteraceae, Vernonieae), of the state of Chiapas, Mexico is described. The new species is distinguished from the species Lepidonia salvinae, which is also distributed in this region, by the presence of white flowers, diversity of trichomes on the phyllaries, the presence of glands at the base of the cypsela and the microsculpture pattern of the outer surface of the cypsela.
Lepidonia S.F. Blake is one of four genera of subtribe Leiboldiinae H. Rob., one of the 21 subtribes of the tribe Vernonieae (Keeley and Robinson, 2009). In the original description, Lepidonia differs from the other genera of Vernonieae by a paleaceous receptacle, like the one present in Bolanosa A. Gray from Mexico and Heterocoma DC. from Brazil (Blake, 1936).
Lepidonia is considered to be a monophyletic group, related to Leiboldia Schltdl, ex Gleason and Stramentopappus H. Rob. & V. A. Funk (Robinson and Funk, 1987; Keeley et al. 2007). However the taxonomic history of the genus has been complicated. Some years after its description as a new genus, Turner (1981) transferred the only described species to the genus Vernonia Schreb., and used the generic name Lepidonia to delimit a section which includes Vernonia paleata (S. F. Blake) B. L. Turner (= Lepidonia paleata S. F. Blake), as well as six other species currently classified in Lepidonia. In a recent study, Turner (2007) kept in section Lepidonia eight species that are currently included in the genus Lepidonia, four of which are endemic to Mexico, one is shared between Mexico and Guatemala, two are endemics from Guatemala and one is endemic to Costa Rica (Redonda-Martinez unpubl. data).
As a product of the constant exploration of the state of Chiapas by the second author, a population that at first instance would correspond to Lepidonia salvinae (Hemsl.) H. Rob. & V. A. Funk was found. However, the individuals of this population present some macroscopic and microscopic characters that allow us to consider it as a new species. One of these characters is the presence of green phyllaries and white corollas (vs. purple phyllaries and corollas, Fig. 1). In this paper the new species of Lepidonia is described and illustrated.
Materials and Methods
Extensive field work was carried out in the state of Chiapas (Mexico) during the winter of 2012 and 2013, which is the flowering season of the species of the genus Lepidonia. Herbarium specimens were collected for further study and deposited in CHIP, GENT, MEXU and other collections.
Fragments of leaves, phyllaries, florets and cypselae were analyzed with a scanning electronic microscope (SEM). The removed material came from herbarium specimens held at the National Herbarium of Mexico (MEXU). The material was washed and hydrated with hot water (85–90°C) for 2 hr, after which it was dehydrated in a successive series of alcohol with concentrations varying from 30–70%, with changes each 2 h. To remove impurities, the samples in 70% alcohol were placed inside microfuge tubes, which were put in a beaker with water and a magnetic stirrer for 24 h. After this we followed the dehydration process to absolute alcohol and then to critical point with 99.8% pure CO2 in an Emitech K850 dryer.
Dried samples of leaves, phyllaries and florets were placed both at abaxial and adaxial view on an adherent double carbon ribbon, fixed on a sample holder, and covered with a gold film of 20 mÅ thick in a Quorum Q150R ES metallizing for 2 min. We repeated this process twice. Consequently, samples were observed in a Hitachi SU1510 SEM at different magnifications using a voltage of 10 kV. Cypselae were placed directly on the adherent double carbon ribbon, and processed the same way as the other structures.
Lepidonia alba Redonda-Martínez & E. Martínez, sp. nov. — TYPE: MEXICO. Chiapas. Municipio de Cacahoatán: 5 km SSE de Agua Caliente 15°8′40″ N, 92°8′47″ W, 2162 m elev., 7 Jan 2012, E. Martínez S. et al. 42631 (Holotype: MEXU!, Isotypes: CHIP!, CTES!, GENT!, IEB!, NY!, US!).
Shrubs 4.0 m high. Stems striate, ferrugineous-pilose. Leaves alternate, petioles 1.5–2.2 cm long, ferrugineous-pilose, blades lanceolate or elliptic-lanceolate, 10.9–17.4 cm long, 2.5– 5.8 cm wide, both surfaces pilose and glandular; leaf base decurrent along the petiole, apex acute or apiculate, margins serrate. Heads 2–4, homogamous, discoid, pedunculate, forming corymbs 2–4 heads, sometimes solitary heads, pedicels 2.6–4.1 cm long, ferrugineous-pilose. Involucre graduate, campanulate, 1.4–1.7 cm long, 1.9–2.3 cm wide; involucral bracts in 5–6 series, oblong, apex very widely ovate mucronate, pilose-glandular, outer series 5.8–6.2 mm long, 4.0– 4.2 mm with, interior series 13.6–15.8 mm long, 2.3–2.7 mm wide. Florets 90–106 per head, white, actinomorphic; corolla 16.0–19.0 mm long, tube 9.0–10.0 mm long, covered with glandular trichomes, lobules 7.0–9.0 mm long, glandular trichomes present especially at the apex, throat poorly defined. Anthers 4.0–5.0 mm long, glabrous, triangular at the apex, sagittate at the base. Style 16.0–18.0 mm long, branches elongate, acute, pilose, 4.0–5.0 mm long. Cypselae oblong, glabrous, 4 or 5 ribbed, 4.0–5.0 mm long. Pappus of capillary bristles, biseriate, deciduous, 6.0–6.6 mm long. Pollen 35–45 µm diameter, subechinolophate, tricolporate, with perforated tectum. Figures 2, 3.
Etymology—The specific epithet refers to the white corolla, which contrasts with the characteristic violet corollas in most species of Vernonieae.
Distribution, Habitat and Ecology—Lepidonia alba is known only from the type collection, a relatively common feature in other species of the genus such as L. corae (Standl. & Steyerm.) H. Rob. & V. A. Funk and L. paleata S. F. Blake. In contrast, the distribution of L. salvinae includes several locations in Chiapas and Guatemala (Fig. 4), a distribution which is similar to that of the toad Incilius tacanensis Smith. L. alba is restricted to mountain cloud forest. The flowering and fruiting period are poorly known, but based on the type specimen flower and fruits can be found from December to January. The distribution of L. alba is similar to other species of plants that are only known from the Tacana Volcano, for example Zinowiewia tacanensis Lundell; Dioscorea tacanensis Lundell; Rhipidocladum martinezii Davidse & R. Pool; Stelis tacanensis R. Solano & Soto-Arenas and Hydrangea steyermarkii Najarro, Samain & E. Martínez.
Morphological Affinities—Lepidonia alba is morphologically similar to other species of Lepidonia and shares with them habit, number of flowers in a head, number of ribs and cypselae shape, and straw-colored deciduous pappus. It is probably closely related to L. salvinae, with which it may be confused. Both species share some morphological characteristics (e.g. phyllary apices with very widely ovate mucronate tips, the number of flowers and cypsela form) and a geographic distribution on Tacana Volcano which is in the middle of the state of Chiapas, Mexico and the middle of the department of San Marcos, Guatemala. The restricted known distribution of L. alba may be due to a lack of collections or a micro endemism of recent origin.
On the other hand, among the differences between L. alba and L. salvinae in addition to the white color of corollas are various micro characters of the new taxon, such as the lack of conic and acicular trichomes on the corolla lobes, the presence of flagelliform trichomes on the phyllaries, presence of glands on the base of cypselae and the alveolate micro sculptural pattern on the cypsela surface (Figs. 5–6, Table 1). Micro characters in generic and specific delimitation have been widely applied in Asteraceae (King and Robinson, 1972). Specifically the taxonomic value of trichomes in delimitation of closely related species in Vernonieae has been tested in several studies (Hunter, 1967; Faust and Jones, 1973; King and Jones, 1975; Redonda-Martínez and Villaseñor-Ríos, 2009), and they are important for defining the new taxon.
RRM thanks Berenit Mendoza-Garfias for the magnificent photographs of scanning electronic microscope and the Posgrado en Ciencias Biológicas of the Universidad Nacional Autónoma de México (UNAM) and Consejo Nacional de Ciencia y Tecnología (CONACyT) for the grant (263523) for postgraduate studies. Itzi Fragoso-Martínez provided valuable comments that greatly enriched the manuscript.
EMMS is grateful to the Mohammed Bin Zayed Species Conservation Fund (project number 11251854) for financial support of Hydrangea research in Mexico, during which this new taxon was discovered. He also acknowledges the Secretaría de Medio Ambiente y Recursos Naturales (SEMARNAT; permit number SGPA/DGGFS/712/3804/ 10) for the permission to collect material; Francisco Javier Jiménez González, Regional Director Frontera Sur, Istmo y Pacífico Sur of the Comisión Nacional de Áreas Naturales Protegidas (CONANP), for permission the to collect within Natural Protected Areas as well as the local CONANP staff members for the help given with logistics and support in the field; the staff of the the herbarium CHIP, Dirección de Botánica Dr. Faustino Miranda in Tuxtla Gutiérrez, Chiapas for support with field and herbarium work and logistics. Ramiro Cruz Durán (Facultad de Ciencias, Universidad Nacional Autónoma de México) is greatly acknowledged for the fast and careful work on the splendid illustration presented here. The authors acknowledge the valuable comments of two anonymous reviewers, which helped improve considerably the manuscript.