On Hydrangea peruviana, an endangered species from Ecuador, and Hydrangea oerstedii, very common in Costa Rica and Panama, and seven threatened Central and South American Hydrangeas, which have been confounded with these Author Samain, Marie-Stephanie https://orcid.org/0000-0002-7530-9024 Red de Diversidad Biologica del Occidente Mexicano, Instituto de Ecologia, A. C., 61600 Patzcuaro, Michoacan, Mexico mariestephanie.samain@gmail.com Author Granados Mendoza, Carolina https://orcid.org/0000-0003-4001-619X Departamento de Botanica, Instituto de Biologia, Universidad Nacional Autonoma de Mexico, 04510, Mexico City, Mexico Author Martinez Salas, Esteban Manuel Herbario Nacional de Mexico, Departamento de Botanica, Instituto de Biologia, Universidad Nacional Autonoma de Mexico, 04510, Mexico City, Mexico text PhytoKeys 2021 2021-01-26 171 91 153 http://dx.doi.org/10.3897/phytokeys.171.56351 journal article http://dx.doi.org/10.3897/phytokeys.171.56351 1314-2003-171-91 08DD30844BC558DB83D270DDFE99A853 5. Hydrangea panamensis Standl., J. Wash. Acad. Sci. 17(1): 10. 1927. Figures 8 , 9 Type. Panama. Colon , along Rio Fato, 10-100 m, floral buds, H.F. Pittier 3919 (holotype: US! [00097000], isotypes: A!, BM! [BM000028808], C!, F! [V0066620F], GH! [00042780], K! [K000486137], NY! [00007170]) floral buds. Description. Root-climbing liana of up to 20 m high, never reaching above the lower branches of its host tree canopy (Fig. 9A ), sometimes bending downwards, functionally dioecious; leaves decussate, petiole sulcate adaxially, terete abaxially, color reddish brown, densely pubescent with caducous, appressed, reddish, stellate hairs, 1-2 cm long, leaving a nearly triangular scar on the branch when leaves fall; lamina obovate to slightly elliptic, 5-12 cm long, 3-6 cm broad, base cuneate to rounded, slightly asymmetric, apex rounded with a very small acumen, leaf margin very slightly glandular-dentate, slightly revolute, venation brochidodromous, veins 4-6 pairs, adaxial leaf side with midvein and primary veins marked, primary veins join to form submarginal vein, pubescent with caducous, appressed, stellate hairs, the basal stalk reddish, the rest whitish, opaque pale green, abaxially with protruding midvein, primary veins alternately protruding and marked, secondary veins marked, regularly with concave cleavages on the junction of primary and secondary veins, opaque pale reddish brown, densely pubescent with appressed, stellate hairs, the basal stalk reddish, the rest whitish, acarodomatia very rare, 0-2 per leaf, consisting of a simple cavity in the axil of the midvein and primary veins; inflorescence axis pubescent with appressed, small, yellow-reddish, stellate hairs, shedding in older specimens, 2-10 cm long, quadrangular, with 1 decussate leaf and 1 kataphyll pair below the inflorescence, rapidly deciduous, apex of the floral axis woody, quadrangular, elongated bract scars visible, thickening at the top, 2-3 mm broad, 1-1.5 mm high in functionally female plants, 2-3 mm broad, 1 mm high in functionally male plants, inflorescence bracts cucullate, membranous, densely pubescent with reddish stellate hairs, veins palmate, bracts increasing in size, lowermost bract 1.5 cm large, 1.1 cm broad, higher bracts up to 2 cm large, 1.6 cm broad, inflorescences lateral, decussate, 1-3 pairs of inflorescences per flowering branch, flowering branch only continues growing very rapidly during inflorescence development, with up to 7 leaf pairs above the inflorescences, giving a very homogeneous aspect, inflorescence axes with basal lignified parts of inflorescences of previous years not observed, leaves or kataphylls present at the base of the inflorescence, inflorescence umbellate (Fig. 9B ), buds up to 2 cm broad and 1.5 cm high before opening, in flowering stage 3-10 cm diameter, 1.5-5 cm high, with 5-8 main axes in functionally male plants, 5-8 main axes in functionally female plants, partial inflorescences racemoid, secondary and tertiary inflorescence axes with yellowish white stellate hairs, pubescence slightly decreasing towards flower insertion; enlarged marginal flowers always present (Fig. 9B ), terminally placed in a raceme, sepals white, yellow or pink, fertile or reduced, when fertile stamens 8, pistils 2, fruit developing, when reduced only sepals developed, central part of the flower amorph, 0.5-0.7 cm diameter when flowering, 1.5-2 cm diameter with mature fruits, pedicel 1.2 cm long when flowering, 1.5-2 cm long with pedicel 1.5-2 cm long with mature fruits; flower pedicel of reduced flowers 0.5-2 mm long in functionally male flowers, 0.5-2 mm long in functionally female flowers, receptacle broadly triangular in functionally male flowers, semiglobose in functionally female flowers, ovary inferior, calyx lobes 4, broadly triangular, 0.2-0.3 mm long, petals 4, white, valvate, cucullate, membranous, 1.5-2 mm long, 1.5-1.8 mm broad; functionally male flowers : hypanthium 1.2-1.8 mm diameter, 0.8-1 mm high, stamens 8, well-developed, filaments 1 mm long, anthers 0.5 mm long, 0.2 mm broad, pistils 2, reduced, 0.1-0.2 mm long, stigmas not penicellate; functionally female flowers : hypanthium 1.5-1.6 mm diameter, 1-1.5 mm high, stamens 8, reduced, filaments 0.5 mm long, anthers 0.1 mm long, 0.1 mm broad, translucent, pistils 2, 1 mm long, enlarging up to 1.8 mm during fruit maturation, stigmas apically clavate and shortly penicellate; fruit a semiglobose capsule, apically with a conspicuous, slightly revolute border, 6-8 well marked ribs, dark reddish brown, 1.5 mm high, 3-3.5 mm broad above, 2 mm diameter, opening between the two pistils to release seeds, seeds not seen. Figure 9. Hydrangea panamensis A plant growing along the stem of a Cecropia B infructescence with young and mature fruits, and enlarged marginal flowers. Hydrangea peruviana C stolons with adventitious roots and decussate leaves. A, B field images of collection Samain & Martinez 2012-063 C field image of collection Granados Mendoza et al. 2012-112 . Distribution. This species is known from Costa Rica and Panama (Fig. 8 ). Habitat. Hydrangea panamensis grows in tropical rainforest between 200 and 1000 m elevation. It usually occurs near water streams at lower elevations. Of all the species of the present study, this is the one that grows at the lowest elevation. Phenology. Hydrangea panamensis has been collected with flowers and fruits between June and September. Notes. Not to be considered a synonym of H. peruviana from which it can be distinguished by the rounded leaf apex with a very small acumen and the very few acarodomatia (0-2/leaf) on the abaxial leaf side vs. the acute to acuminate, rarely mucronate leaf apex and the many acarodomatia (present in both axils of midvein and primary veins and those of primary and secondary veins) of H. peruviana . Moreover, their known distribution areas are far away from each other, with H. panamensis only growing in Central America and H. peruviana being endemic to Ecuador. The label of the specimen Gentry 5569B mentions that the flowers are red, whereas the label of the specimen Mori & Bolten 7674 says "summit of ovary of fertile flowers reddish-pink". It seems there is some color variation in this species in both the marginal and reduced flowers. Both flower types are generally white, and this is also the color we have observed in the field ourselves. According to our molecular study, Hydrangea panamensis is closely related to H. peruviana (Granados Mendoza et al. unpublished results). Preliminary conservation status. Although this species has an EOO of about 50,123 km2, it is Endangered according to the IUCN categories and criteria ( IUCN 2012 ), with an AAO of 60 km2, as well as an extensive reduction in both EOO and AOO as a consequence of habitat destruction and fragmentation. Additional specimens examined. Costa Rica. Puntarenas : Golfito, Playa Cacao, Cuenca Superior de Quebrada Nazareno, 8°37'50"N , 83°11'30"W , 200 m, 11 Jun 1994, ♂, flowers, Herrera & Rivera 7152 (CR, F, K, MO); Golfito-La Gamba (km 37), gap by the waterfall - Sendero Ozelot near the Rainforest Lodge, 8°41'N, 83°13'W, 70-300 m, 20 Jun 1997, inflorescence buds, Weissenhofer W105 (CR, WU); Golfito, Bosque de los Austriacos, Fila Gamba, Avilan woodcutter way, 8°41'N , 83°13'W , 250 m, 3 Jun 1997, ♂, old flowers, Huber & Weissenhofer 747-3.6.97 (CR); Osa, al lado del camino Rincon-Bahia Drake, 2.23 km al ONO de Rancho Quemado, 8°41'35.39"N , 83°35'7.42"W , 237 m, 8 Aug 2012, ♀, fruits, Samain & Martinez 2012-063 (CR, GENT, IEB, MEXU); Cerro Anguciana, cabeceras del Rio Piedras Blancas, 4.96 km al NE de Piedras Blancas, 8°48'27.49"N , 83°12'18.05"W , 676 m, 9 Aug 2012, ♀, fruits, Samain & Martinez 2012-064 (CR, GENT, IEB, MEXU). Panama. Darien : Cana and vicinity, 2000-6500 ft, 7 Apr 1908-8 Jun 1908, old inflorescence branches, Williams 775 (NY); Cocle : between Cerro Pilon and el Valle de Anton , 700-900 m, 15 May 1967, ♀, flowers, Duke & Dwyer 13952 (MO); region north of El Valle de Anton, 1000 m, 27 Sep 1946, ♀, fruits, Allen 3712 (E, GH, F, MO, P, UPS); alrededores de El Valle de Anton , Altos de La Mesa, 1.3 km al N de la bifurcacion hacia Rio Indio, 8°38'38" N , 80°06'51"W , 735 m, ♂, flowers, 13 Aug 2014, Galdames et al. 7676 (PMA); Distrito La Pintada, cerca de las cabanas de ANAM, 8°40'05"N , 80°35'34"W , 800-900 m, 14 Aug 2007, ♀, fruits, Hernandez et al. 528 (PMA); Panama : Canal Zone, Barro Colorado Island, E. Of Wheeler 13, 18 Aug 1970, ♀, flowers, Foster 1797 (DUKE, F, PMA, UC); Barro Colorado Island, forest 200 m E of Wheeler Trail 1300, 18 Aug 1970, ♀, fruits, Croat 11850 (AAU, DUKE, E, F, MO); pipeline road, 14 Sep 1971, ♀, fruits, Gentry 1792 (DUKE, F, GH, MO); Panama , North of El Llano, 500-800 m, 25 Jul 1972, ♀, flowers, Gentry 5569B (MO); Cerro Campana, 45 km SW of Panama City on Inter-American Hwy, 8 Aug 1975, ♀, fruits, Mori & Bolten 7674 (AAU, MO); Distrito de Capira, Parque Nacional Altos de Campana, Sendero de Interpretacion , 8°40'54"N , 79°55'40"O , ca. 750 m, 23 Aug 1990, ♀, fruits, Galdames 880 (PMA); Parque Nacional Altos de Campana, Sendero de interpretacion , 1 km al este del campamento de los guardaparques de INRENARE, parcela 10-8, 8°40'N , 79°55'W , 800-900 m, 19 Aug 1993, ♂, flowers, Correa & Montenegro 9780 (PMA, UCH).