Scaevola rialagartensis Cast., 2019

Castillo-Campos, Gonzalo, García-Franco, José G. & Martínez, M. Luisa, 2019, Scaevola rialagartensis (Goodeniaceae), a new species from coastal sand dunes of Rio Lagartos, Yucatan, Mexico, Phytotaxa 392 (3), pp. 239-244 : 240-243

Scaevola rialagartensis Cast. -Campos, sp. nov. ( Figs. 2–3 )

Type:— MEXICO. Yucatan: Rio Lagartos, Rio Lagartos beaches, east of the town of Rio Lagartos 21°30’54’’–87°41’05”, 0 m, 9 October 2018, G. Castillo-Campos & J. J. Pale P. 29321 (holotype XAL!; isotypes CICY!, ENCB!, MEXU!) .

Diagnosis.—This taxon is similar to S. taccada , a species used as an ornamental plant in hotel areas across the American continent; the new taxon grows sympatrically with S. plumieri on the beaches of Rio Lagartos, Yucatan, Mexico. However, S. rialagartensis differs in the size of shrubs, shape of leaf apex, and type of leaf venation ( Table 1).

Shrubs 1–2.3 m in height, usually prostrate. Stem 4 cm in diameter at the base of the main trunk, cylindrical, succulent; brown, occasionally yellow or greenish; with numerous foliar scars on branches. Branches prostrate on the sand. Leaves alternate, arranged spirally around the stem, often revolute; lower leaves deciduous, upper or terminal leaves mostly clustered near the apex of branches; ovate to broadly spatulate, 7.1–22 × 4.5–8.1 cm; fleshy; margin entire, apex slightly obcordate to truncate; base narrow; bearded-canescent axillary, glabrous on the upper and under surfaces; glands at some tips of secondary venation that reaches the margins when fresh but lost upon drying; venation reticulate with 8–13 pairs of lateral nerves; midrib prominent on the lower surface, printed in the upper surface; secondary venation prominent on the lower surface, visible on the upper surface; petiole winged, 5–12 mm long. Inflorescences paniculate, 4–6 cm long. Involucral bracts triangular, 2 × 0.5 mm, glabrous externally, bearded-canescent axillary. Peduncles axillary, 20–25 mm long, 1 mm thick, glabrous. Flowers 3–12 per inflorescence, pedicels 1.5–6.5 mm long, 0.3–0.5 mm thick. Chalice perennial, 5 sepals separated from the base, occasionally inserted, subulate, 2–3 × 0.5–1 mm, glabrous. Corolla white, woolly internally, 1.5–2.3 cm long; lobes 5(6), whitish, divided by the upper half of the corolla tube, linear to lanceolate, subacute, 7–8 × 1–1.8 mm; margin wide, membranous, crenulated; tube 8–9 mm long, 1.5 mm thick, villous internally, glabrous externally, open laterally from its base. Stamens 5, 10 mm long, 0.2–0.3 mm thick. Anthers separate or connivent, attached at base, 2–2.5 mm long, 0.5 mm wide. Style 10 mm long, greenish, pubescent, incurved, with cup-shaped indusium surrounding the stigma; villous-canescent, 1–1.5 mm in diameter. Fruit a drupe, ovate or globose, fleshy, glabrous, 0.8–1.7 cm long, white when ripe, succulent. Seeds nut-shaped, brown, 0.6–0.7 cm long, 0.4–0.5 cm wide; raphe surrounding the seed lengthwise; testa woody, muriculate, covered by two layers: the outer fleshy; the inner, by a spongy aril.

Geographic distribution and ecology:—After a recognition survey to islands and coastal dunes of the Ria Lagartos Biosphere Reserve in the state of Yucatan, Mexico, collecting the most common species, some individuals of Scaevola rialagartensis , probably endemic to this region of Mexico, were found growing at the edge of the mangrove forest at an altitude of 0 to 1 m.

Scaevola rialagartensis is a species of shrub vegetation growing along coastal dunes, along the edges of mangrove forests on white sandy soils, at an altitude of 2 m a.s.l., mainly on coastal dunes of the Rio Lagartos beach. Based on the Köppen climate classification, the coastal zone of Yucatan presents a strip of BS (dry or arid) climate, with some variations characterized by scarce rains and high temperatures ( Orellana et al. 1999). According to 1971–2000 records of the National Meteorological System, the El Cuyo weather station records a rainfall of 779 mm per year and an mean annual temperature of 26.8 °C ( Torres et al. 2010).

Adult individuals of the new taxon reach up to 2.30 m high. They occur together with Atriplex canescens ( Amaranthaceae ), Avicennia germinans ( Acanthaceae ), Bidens pilosa ( Asteraceae ), Canavalia rosea ( Fabaceae ), Cassytha filiformis ( Lauraceae ), Coccoloba uvifera ( Polygonaceae ), Conocarpus erectus ( Combretaceae ), Distichlis spicata ( Poaceae ), Ernodea littoralis ( Rubiaceae ), Ipomoea pes-caprae ( Convolvulaceae ), Lantana involucrata ( Verbenaceae ), Scaevola plumieri ( Goodeniaceae ), Sesuvium portulacastrum ( Aizoaceae ), Sporobolus virginicus ( Poaceae ), Suriana maritima ( Surianaceae ), Tournefortia gnaphalodes ( Boraginaceae ), Tribulus cistoides ( Zygophyllaceae ), Rhizophora mangle ( Rhizophoraceae ), Waltheria indica ( Malvaceae ).

Etymology:—The name of the new species refers to the locality Rio Lagartos, Yucatan, an area where it grows and where the type specimen was collected.

Phenology: — Scaevola rialagartensis flowers from May to November and produces fruits from July to December.

Additional species examined:— MEXICO. Yucatán: Rio Lagartos, Rio Lagartos beaches, W of the town of Rio Lagartos, G. Castillo-Campos & J.G. García-Franco 29313.

Scaveola rialagartensis is sympatric with S. plumieri and resembles S. taccada . Both species can be differentiated by shrub size, leaf apex shape, and type of leaf nervation ( Table 1).

The restricted distribution of S. rialagartensis in the Yucatan Peninsula includes areas that are currently under heavy disturbance and threatened by tourism and urbanization. Therefore, preserving and protecting the habitat where the species thrives is of the utmost importance. This species is parasitized by Cassytha filiformis L. ( Lauraceae ), an invasive species in coastal dunes in the type-locality areas. Due to its highly restricted distribution, low abundance, and potential threats, this species should be considered for inclusion in some protection category (i.e., subject to legal protection) in the Mexican Official Standard (NOM-59-SEMARNAT-2010) and on the list of endangered species issued by the International Union for the Conservation of Nature (IUCN).

Figures

FIGURE 2. Illustration of Scaevola rialagartensis. a, portion of the habit; b, branch with flowers and fruits; c, detail of the leaf; d, portion of the inflorescence; e, flower with stigma details; f, stamen, g, portion of the infrutescence; h, fruit, longitudinal section; i, seed covered with the aril; j, seeds. Illustration by Edmundo Saavedra based on the holotype specimen G. Castillo-Campos & J.J. Pale P. 29321.

FIGURE 3. Scaevola rialagartensis Cast.-Campos sp. nov. in its habitat. a) shrub lying on the sand dune and parasitized by Cassytha filiformis L.; b) branch with inflorescences, flowers in anthesis, and revolute leaves. (Photos G. Castillo-Campos).