Hydrangea caucana Engl., Nat. Pflanzenfam. (ed. 2) 18a: 206. 1930., Engl., Nat. Pflanzenfam. (ed. 2) 18 a: 206. 1930.

Samain, Marie-Stephanie, Granados Mendoza, Carolina & Martinez Salas, Esteban Manuel, 2021, 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, PhytoKeys 171, pp. 91-153: 91

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Hydrangea caucana Engl., Nat. Pflanzenfam. (ed. 2) 18a: 206. 1930.


1. Hydrangea caucana Engl., Nat. Pflanzenfam. (ed. 2) 18a: 206. 1930.   Figures 1 View Figure 1 , 2 View Figure 2


Colombia. Cauca: Caldas, Las Pavas Cimarronas, 1200-1600 m, ♀, flowers, F.C. Lehmann 5106 (lectotype, designated by McClintock 1957, pg. 240 [as “isotype”], second-step designated here: K! [K000486133], isolectotypes: F! [F0066623F], K! [K000486134].


Root-climbing liana of probably not more than 15-20 m high; functionally dioecious; free-growing branches slightly quadrangular, densely pubescent with reddish brown stellate hairs; leaves decussate, petiole sulcate adaxially, terete abaxially, color reddish brown, densely pubescent with caducous, reddish-brown, stellate hairs, 0.6-1.5 cm long, leaving a semicircular scar on the branch when leaves shed; lamina flat, ovate to lanceolate-elliptic, 6-12 cm long, 2.6-5.5 cm broad, base rounded to decurrent, sometimes asymmetric, apex acuminate, leaf margin glandular dentate, teeth generally small, larger in only a few leaves, venation brochidodromous, veins 5-7 pairs, adaxial leaf side with marked midvein, primary and secondary veins lightly marked, primary veins join to form submarginal vein, sparsely pubescent with appressed, white stellate hairs, in young leaves more dense and reddish hairs, abaxially with protruding veins, primary veins sometimes alternating protruding and marked in the same leaf, dark brown green, densely pubescent with appressed stellate reddish hairs near the midvein, rest of the lamina more sparsely pubescent, acarodomatia present, numerous, consisting of a simple cavity, but often not very conspicuous as they lay hidden under the midvein pubescence, in axils of midvein and primary veins; inflorescence axis densely pubescent with persistent reddish brown, stellate hairs, more dense towards the apex, 8-21 cm long, many-ribbed, with up to 3 opposite or decussate leaf pairs and up to 3 scars of possibly kataphyll pairs below the inflorescence, deciduous, petiole 5-15 mm long, lamina 6-12.5 cm long, 2.5-5.5 cm broad, kataphylls not seen, apex of the floral axis woody, basally quadrangular, apically triangular, elongated bract scars visible, 3-4 mm broad, 1.5-2 mm high in functionally female plants, 3.5-5 mm broad, 2-2.5 mm high in functionally male plants, inflorescence bracts cucullate densely pubescent, hairs reddish-brown, stellate, increasing in size, lowermost bract 1.5 cm large, 1.2 cm broad, other bracts not visible, inflorescences lateral (Fig. 1 View Figure 1 ), decussate, 1-3 pairs of inflorescences per flowering branch, flowering branch only continues growing vegetatively rapidly during inflorescence development, with up to 6 leaf and kataphyll pairs above the inflorescences, inflorescence axes with basal lignified parts of inflorescences of previous years not seen, kataphylls at the base of the inflorescence present, orbicular, inflorescence umbellate, buds not seen, in flowering stage 4-12 cm diameter, 2.5-7 cm high, with 6-9 main axes in functionally male plants, 6-8 main axes in functionally female plants, partial inflorescences cymes, secondary and tertiary inflorescence axes densely pubescent with reddish, stellate hairs, pubescence gradually decreasing towards flower insertion; enlarged marginal flowers always present, terminally placed in a cyme, sepals 4, separate, with marked veins, pistils 2, fertile or reduced, some flowers with mature fruit, in these cases only 1 sepal visible, 1.5-2.3 cm diameter, pedicel 1-2 cm long, reddish-purple; flower pedicel of reduced flowers, 0.2-1.5 mm long in functionally male flowers, 0.5-2(-3) mm long in functionally female flowers, receptacle triangular in functionally male flowers, semiglobose in functionally female flowers, ovary inferior, calyx lobes 4, triangular in male flowers, nearly reduced to zero in female flowers, enlarging during fruit maturation, reduced, petals 4, bright red to purple, cucullate, 1.2 mm long; functionally male flowers: hypanthium 1-1.2 mm broad, 0.8-1 mm high, stamens 8, well-developed, pink, filaments 0.5-1.5 mm long, anthers 0.5 mm long, 0.2 mm broad, pistils 2, reduced, 0.2 mm long, stigmas not penicellate; functionally female flowers: hypanthium 1 mm diameter, 0.5 mm high, stamens 8, reduced, filaments and anthers together 0.2 mm long, pistils 2, 0.5-0.8 mm long, enlarging up to 2 mm during fruit maturation, stigmas slightly apically clavate and shortly penicellate; fruit a semiglobose capsule, apically with a thickened border, dark reddish brown, 0.8-1.2 mm high, 1.5 mm broad above, 1.5 mm diameter, opening between the two pistils to release seeds, seeds not seen.


This species is endemic to Colombia and currently only known from the departments of Antioquia, Nariño and Valle de Cauca (Fig. 2 View Figure 2 ).


Hydrangea caucana   is known from mountain cloud forest at elevations between 750-1365 m.


Hydrangea caucana   has been collected with flowers and fruits between November and March.


McClintock (1957) cited the K material as lectotype albeit without designating a specific sheet, which was copied by Freire-Fierro (2004). The holotype in B was destroyed; a photo of this specimen is available in F. We here select the better of the two sheets at K in a second-step lectotypification.

Hydrangea caucana   should not be considered a synonym of H. peruviana   and can be distinguished from the latter species by the flat, ovate to lanceolate-elliptic leaves with a glandular dentate margin. In contrast, H. peruviana   is characterized by very slightly spoon-shaped, elliptic to slightly obovate leaves with a serrate to slightly dentate margin. Moreover, H. caucana   is currently only known from Colombia, whereas H. peruviana   is restricted to Ecuador.

We have not observed this species in the field, and herbarium labels of the known specimens of H. caucana   do not record the size of the plants.

The phylogenetic relationships of Hydrangea caucana   are yet unknown as there was no fresh material available for our molecular study (Granados Mendoza et al. unpublished results).

Preliminary conservation status.

Based on the available herbarium collections, this species is Endangered according to the IUCN categories and criteria ( IUCN 2012), with an AAO of 32 km2, fewer than five locations and an extensive reduction in both EOO and AOO due to habitat destruction and fragmentation. The most recent collection of this species we have seen is from 1992, so further exploration is needed to know the current distribution and conservation status of this species.

Additional specimens examined.

Colombia. Antioquia: Urrao, Aguadas, 1300 m, 8 Dec 1992, sterile, Pipoly et al. 16776 (MO); Frontino, Vereda Venados, Parque Nacional Natural Las Orquídeas, margen izq. Río Venados (Garrucha y Alto Bonito), 6°32'N, 76°19'W, 800-850 m, 30 Jan 1995, ♂, flowers, Pipoly et al. 18117 (MO, NY); same data as preceding, Parque Nacional Natural las Orquídeas, sector Calles, margen derecha del Río Calles, 1310-1365 m, ♀, fruits, 27 Mar 1988, Cogollo et al. 2669 (COL, MO); same data as preceding, 1360 m, ♂, flowers, 19 Feb 1989, Cogollo et al. 4091 (MO); Nariño: Mpio. de Ricaurte, Resguardo Indígena Nulpe Medio, camino a la quebrada La Conga, 1°6'N, 78°13'W, 750 m, 8 Jan 1996, ♂, flowers, González & Ramírez 1636 (QCA); municipio Barbacoas, corregimiento Altaquer, Vías Las Vegas, al borde del río Veza, 870 m, flower buds, Mar 1995, Fernández et al. 12459 (COL); Valle de Cauca: Cordillera Occidental, vertiente occidental, Hoya del Río Digua, lado derecho, La Elsa, 1000-1200 m, 9 Nov 1943, ♀, flowers, fruits, Cuatrecasas 15326 (F, P, US); Cordillera Occidental, vertiente occidental, Hoya del Río Digua, lado derecho, entre Queremal y La Elsa, 1200-1160 m, ♀, 27, 29 Mar 1947, ♀, flowers, Cuatrecasas 23994 (F, US).