Casearia isthmica de Mestier & O.Ortiz, 2023

de Mestier, Astrid, Campos Pineda, Ernesto, Cedeno Fonseca, Marco & Ortiz, Orlando O., 2023, A new species of Casearia Jacq. (Salicaceae) from Central Panama and insights into its phylogenetic position within the genus, PhytoKeys 236, pp. 97-112 : 97

Casearia isthmica de Mestier & O.Ortiz sp. nov.

Figs 3 , 4

Type.

Panama. Distrito de Capira: Parque Nacional Altos de Campana, sendero La Rana Dorada , ca. 100 m desde la entrada, 8°41'32"N, 79°55'34"W, 839 m, 27 April 2022, E. Campos & J. Sumich 1329 (SAL302) (holotype: PMA-127644!; isotypes: B-101233230!, SCZ! two sheets, barcodes: 20033 and 20034) .

Casearia isthmica shares morphological similarities with C. laetioides (= Zuelania guidonia (Sw.) Britton & Millsp), C. sanchezii and C. tremula . From both the plastid and nuclear trees, C. laetioides can be hypothesized as sister species to the newly discovered C. isthmica . In terms of morphology, this new taxon differs from C. laetioides (A. Rich.) Northr. by having essentially glabrous leaf blades (vs. pubescent), a prominent style (vs. absent or sometimes poorly developed), greenish-white sepals (vs. yellowish), 12 staminodia and stamens (vs. 15-20 staminodia and 20-40 stamens), and glabrous fruits (vs. pubescent). Furthermore, C. sanchezii differs morphologically from C. isthmica in presenting sessile inflorescence, crenate to subentire leaf blade and a longer petiole of 1 to 2.5 cm. C. isthmica differs from C. tremula in having congested inflorescences with 12-20 flowers (vs. loose inflorescences with 3 to 10 flowers), 12 stamens arranged in one row (vs. 15 to 24 stamens in two rows), and pubescent styles (vs. glabrous). The discriminating morphological characteristics between C. isthmica and its congeners were listed in Table 1 . C. sanchezii is found in the cloud forest of Mexico and El Salvador at elevation of 1600 to 2000 m, whereas C. isthmica is endemic to Central Panama and occurs at 800 m.

Description.

Tree, up to 1520 m tall; trunk straight, with bark cream, highly lenticellate; linear lenticels, arranged horizontally and vertically; branches zig-zag in shape, brownish, glabrous, with white lenticels. Stipules 4.0-6.8 × 2.5-4 mm, glabrous, ovate or triangular, persistent on the upper part (distally) and then deciduous. Leaves alternate, simple, deciduous when flowering; petiole 0.5-0.8 cm, canaliculate, glabrous; leaf blade 3.5-8.8 × 0.7-2.6 cm, subcoriaceous or coriaceous, drying brownish or blackish, lanceolate to obovate, asymmetrical, rounded or sometimes acute at the base, subcaudate-acuminate at the apex, densely pellucid punctate, glabrous on both sides, although slightly puberulous on the major abaxial veins; margins slightly serrate to crenate, marginal teeth more frequent in the upper half of the leaf blade; venation pinnate, lateral secondary veins in 5-10 ascending pairs, higher-order veins forming a dense reticulation, prominent on the abaxial surface. Inflorescences pedunculate, congested, umbeliform, each unit 12-20 flowered; peduncle 3 mm; bracts ca. 3.2 mm, coriaceous, ovate-lanceolate, greenish; pedicels ca. 8 mm, terete, basally articulate, green, glabrous. Floral buds oblong-obovate; flowers bisexual; sepals 5, ca. 4.0 × 1.6 mm, seemly free, oblong-obovate, glabrescent, greenish-white, white internally and greenish externally; staminodia 12, white, ligulate, white-hirsute; stamens 12 on the same row as the smaller staminodia and alternating with them, densely pubescent; filaments equal, free, white-hirsute; anthers elliptic, creamy, white-hirsute externally; ovary greenish, ovate, white-hirsute; style undivided, white-hirsute; stigma capitate, creamy. Fruits fleshy, orbicular, up to 5 cm diameter, very glossy, green during development, turning black-purple externally and pinkish or red internally when ripe, covered on the lower part by the sepals, dehiscent by 3 valves; seeds many, creamy-white, aril orange.

Distribution and habitat.

Endemic to Central Panama ( Panamá and Panamá Oeste provinces) (Fig. 5 ), documented only from cloud forests at elevations between (600-)800-900 m, in the premontane rain forest life zone.

Phenology.

Flowering in April, May. Fruiting in June, July.

Etymology.

The specific epithet refers to the geographic distribution of the new species, which is restricted to the Isthmus of Panama.

Preliminary conservation status.

Casearia isthmica is known from ten collections made in two locations (Altos de Campana and Altos de Pacora). These collections were made within or very close to the external limits of protected areas (Altos de Campana National Park and Chagres National Park). Although they are protected areas, both locations face moderate anthropic disturbances, mainly in the borders such as Altos de Pacora (Chagres National Park). The highest threat facing this taxon is the loss of habitat caused by new road constructions and building of housing, as well as destructive tourist activities that are not environmentally sustainable, such as clandestine motorcycle races through the forest. Because this species has a limited distribution (EOO: 220 km2; AOO: 16 km2), the effect on its natural habitat may be extremely critical and may compromise its conservation. Casearia isthmica must be considered as Endangered [EN B1ab(iii)+2ab(iii)].

Selected specimens examined.

Panama Panamá Oeste Province: Parque Nacional Altos de Campana; Sendero de Interpretación; 1 km del campamento de los guardaparques de INRENARE; bosque muy húmedo tropical premontano; Camino Zamora ; 8°40'N, 79°55'W; 800-900 m; fl; 21 May 1992; M.D. Correa et al. 8944 (PMA) • Parque Nacional Altos de Campana ; colectado a 5 m de la orilla de la carretera dentro del parque; 8°40'N, 79°55'W; 800-900 m; fr; 24 June 1993; M.D. Correa & E. Montenegro 9622 (PMA) • Parque Nacional Altos de Campana ; Finca García; 8°40'N, 79°55'W; 800-900 m; fr; 28 July 1994; M.D. Correa & E. Montenegro 10717 (PMA) • Parque Nacional Altos de Campana ; 3 agosto 1995; E. Montenegro 1112 (SCZ) • Parque Nacional Altos de Campana ; Las Nubes; División Continental entre Finca de Tomas Herrera ; 600-700 m; 3 May 1997; M.D. Correa et al. 11430 (F; MO PMA) • Parque Nacional Altos de Campana ; Sendero El Tigre; bosque nuboso; 8°40'N, 79°55'W; 900 m; fr; 11 Jul 1998; C. Galdames; E. Montenegro & H. Valdéz 4317 (F; PMA; SCZ) • Distrito de Capira ; Parque Nacional Altos de Campana ; colectado en el sendero de la Rana Dorada; ca. A 100 m de la entrada; 8°41'32"N, 79°55'34"W; 839 m; fl; 3 May 2018; E. Campos & C. Galdames 1087 (B; SCZ) • Distrito de Capira ; Parque Nacional Altos de Campana ; sendero La Rana Dorada; ca. 100 m desde la entrada; 8°41'32"N, 79°55'34"W; 839 m; fl; 27 April 2022; J. Sumich & E. Campos 151 (SCZ) • Distrito de Capira ; Parque Nacional Altos de Campana ; 27 April 2022; sendero La Rana Dorada; J. Sumich 127 (SCZ) . Panamá Province: Cerro Pelón; finca del Sr. Rodrigo Coba; reserva boscosa privada; adyacente a Cerro Jefe ; 9°12'29"N, 79°22'33"W; 825 m; fr; 29 June 2010; C. Galdames; R. Vergara & F. Rodríguez 6642 (PMA; SCZ) .

Figures

Figure 3. Casearia isthmica de Mestier & O. Ortiz A flowering branch B inflorescence C flowers at anthesis D fruiting branch E leaves F ripe fruit G bark. Photos A, C, E (back side of the leaf) by Carmen Galdames (Galdames 6153). Photos D, E (front side of the leaf) by Carmen Galdames (Galdames 6642). Photo B by Ernesto Campos (Sumich 151). Photos G, E by Ernesto Campos Plate by Marco Cedeno-Fonseca.

Figure 4. Casearia isthmica de Mestier & O. Ortiz A branches B twig and stipules C trunk base and roots D lenticellate bark. Photos A, B by Carmen Galdames (Galdames 6642). Photo C by Ernesto Campos (Campos 1087). Photo D by Ernesto Campos. Plate by Marco Cedeno-Fonseca.

Figure 5. Geographic distribution of Casearia isthmica.