Hydrangea steyermarkii Standl.

Samain, Marie-Stéphanie, Najarro, Francisco Hernández & Salas, Esteban Manuel Martínez, 2014, First record of the critically endangered Hydrangea steyermarkii Standl. (Hydrangeaceae) in Mexico, and description of a new widespread Hydrangea species of Mesoamerica, Phytotaxa 162 (4), pp. 181-197 : 190-193

Hydrangea steyermarkii Standl. , amended description, Figs. 2 , 3 , 5

TYPE: - GUATEMALA. San Marcos: Along Quebrada Canjulá , between Sibinal and Canjulá, Volcán de Tacaná, 2200–2500 m, 18 February 1940 , J. A. Steyermark 36044 ( F!, GH! (photo)) [functionally female, immature fruits].

Root-climbing liana of up to 30 m high, functionally dioecious. Main stem clinging to the host tree with many large adventitious roots, up to 12 cm diameter, bark dark brown to black, with reddish lenticels. Runner shoots (stolons) dark brown, fibrous, with adventitious roots and stellate hairs, with small leaves. Branches many-ribbed, with reddish pubescence and adventitious roots, cortex brownish-reddish, contracting, forming corchy patches ( Fig. 2C ), notorious line between petioles of opposite leaves. Petiole sulcate adaxially, terete abaxially, reddish pubescent, sparsely pubescent with short hairs in young stage, glabrous in mature stage, 1.5–3 cm long, leaving a semicircular scar on the branch when leaves fall. Leaves decussate, lanceolate-obovate, base cuneate to slightly rounded, sometimes slightly asymmetric, 10–18 cm long, 4.5–6 cm broad, apex acute to acuminate, leaf margin crenate with marked glandular teeth, especially notorious in leaves of young branches and of stolons, venation brochidodromous, veins 8–9, adaxial leaf side with protruding tertiary veins forming areole, secondary veins end in the glandular teeth, abaxially with protruding primary and secondary veins in young leaves, sunken in mature leaves, tertiary veins well defined in young leaves, invisible in mature leaves, glabrous, abaxial leaf side sparsely whitish pubescent on midvein to pubescent allover the surface, with whitish stellate adnate hairs, shiny dark green, young leaves red-brown, but glands green, with whitish indument ( Fig. 2D ), all veins reddish-brownish, acarodomatia form cavities between midvein and primary veins, sometimes even in between primary and secondary veins. Inflorescence axis with reddish stellate hairs, 7 cm long, with two small decussate leaf pairs below the inflorescence, petiole 1 cm long, lamina 2–3.5 cm long, apex of the floral axis not visible, inflorescence bracts rapidly deciduous, decussate, about 8, of different sizes, consecutively and rapidly caducous during inflorescence development, with whitish to reddish, adnate, stellate hairs, including margin, inflorescences lateral, opposite, two per flowering branch which continues growing vegetatively during inflorescence development, with up to four leaf pairs above the node where the inflorescences originate in the axil of a leaf pair with reduced petiole (0.6–1.5 cm) and without lamina, these ‘leaves’ caducous, only present at the base of inflorescence buds, leaving a scar at the base of mature inflorescences, corymbous, 5 cm diameter, 2–3 cm high, with 5–6 partial inflorescences (corymbs) which on their turn again consist of several corymbs, secondary and tertiary inflorescence axes with reddish stellate hairs. Flower pedicel 0.8–2 mm long, receptacle campanulate in functionally male flowers, broadly semiglobose in functionally female flowers, 2 mm long, ovary inferior, calyx lobes 4, triangular with rounded apex, 1 mm long, petals 4, white, valvate, cucullate, coriaceous, smooth adaxially and abaxially, 1.2–2 mm long, 1,2 mm broad, functionally male flowers ( Figs. 3 D, E, F , 5 B ): hypanthium 2–2.5 mm diameter, stamens (6–)8(–9), welldeveloped, filaments 1.5–2 mm long, anthers 0.7–0.8 mm long, 0.5 mm broad, pistils 2, reduced, 1–1.2 mm long, remnants of ovules present, functionally female flowers ( Fig. 5 C ): stamens in the only available female specimen shriveled as this specimen has only nearly mature fruits, pistils 2, not seen in fertile stage, enlarging up to 3–4 mm in mature fruits, stigmas apically clavate and shortly penicellate, fruit a broadly semiglobose capsule, lateral ribs cannot be distinguished because of the shriveled state of the fruits, dark brown, 3–4 mm high, 4–5 mm broad above, 3–4 mm diameter, opening between the two pistils to release seeds, seeds not seen.

Habitat: ―Very deep valleys in cloud forest (“selva mediana perennifolia” according to Miranda & Hernández X., 1963, “bosque mesófilo de montaña” according to Rzedowski, 1978) dominated by Hedyosmum mexicanum . This species gets easily established in primary forest on very steep slopes in ravines where there are recurrent disturbances as a consequence of very strong winds which cause treefall. This species occurs in conserved localities, as well as on disturbed places with very strong succession dynamics, protected from the humid winds from the south, on igneous rocks, with approximately 3000 mm rainfall.

Distribution: ―South-facing slopes of the volcano Tacaná in México and Guatemala, between 2200 and 3000 m.

Phenology: ―This species has been observed flowering in September and fruiting in February.

Observations: ―The population on the Mexican side of the volcano Tacaná near the village of Chiquihuite, 5– 6 km in straight line from the type locality, is the first record of this species in Mexico. Interestingly, the type specimen belongs to a functionally female individual, whereas our collection is a male specimen. Despite extensive explorations on the Mexican side of the volcano Tacaná, it has not been possible to encounter a female specimen. In contrast to the description, which mentions as habit a climbing epiphytic shrub (‘ frutex scandens epiphyticus ’; Standley 1940: 233), this species is a root-climbing liana.

Standley (1940), in the description of H. steyermarkii , mentions a dense reddish pubescence for the branches (‘ quoque pilis stellatis brunnescentibus laxe tomentosis ’). Nevertheless, this reddish ‘indument’ is a mixture of young adventitious roots and penicellate, stellate hairs. In contrast, the indument on the lamina is whitish on the type specimen and all other studied collections.

The marginal vein is closer to the leaf margin than in H. albostellata . The apex of the leaves on the terminal branch of M.S. Samain et al. 2012-009 and M.S. Samain et al. 2012-010) is acuminate.

The majority of the available herbarium specimens of Guatemala, Honduras, El Salvador and Nicaragua as well as a few collections of Costa Rica bear the identification of H. steyermarkii . However, only the specimens mentioned below coincide with the type of this species and nearly all other specimens belong to H. albostellata .

The number of stamens in the observed functionally female flowers is variable although the average number is 8 with 6 large stamens and 2 smaller stamens. When there are only 6 stamens, they are all of the same size.

Additional specimens examined: ― GUATEMALA. San Marcos: Río Vega , near San Rafael and Guatemala- Mexico boundary, Volcán de Tacaná, 2500–3000 m, J. A. Steyermark 36250 ( F) [sterile]; between Canjulá and La Unión Juárez, near southeast portion of Volcán de Tacaná, 2000–3000 m, slopes of Río Tonaná , J. A. Steyermark 36411 ( F) [sterile]; El Progreso: between Finca Piamonte and top of Montaña Piamonte, along Joya Pacayal, 2500– 3000 m, J. A. Steyermark 43635 (US!); Quezaltenango: western slopes of Volcán Zunil, opposite Santa María de Jesús , 1500 m, 21 January 1940, J. A. Steyermark 35109 ( GH! (photo of F specimen)); Huehuetenango, Cerro Huitz, between Barillas and Mimanhuitz, Sierra de los Cuchumatanes, 1600–2600 m, 14 July 1942, J. A. Steyermark 48536 ( US!) [sterile]; wet cloud forest at Cruz de Limón , between San Mateo Ixtatán and Nucá, Sierra de los Cuchumatanes; 2600–3000 m, 31 July 1942, J. A. Steyermark 49826 (US!) [sterile] . MEXICO. Chiapas: Cacahoatán, Volcan Tacaná, Chiquihuite, 15°6'23.07"N, 92°6'9.13"W, 2362 m, 3 September 2012, M. S. Samain et al. 2012-078 ( CHIP!, GENT!, MEXU!) [functionally male]; loc. cit., 15°6'24.83"N, 92°6'4.25"W, 2476 m, 4 January 2012, M. S. Samain et al. 2012-008 ( GENT!, MEXU!) [sterile]; loc. cit., 15°6'25.1"N, 92°6'4.11"W, 2481 m, 4 January 2012, M. S. Samain et al. 2012-009 ( GENT!, MEXU!) [sterile]; loc. cit., 15°6'23.23"N, 92°6'7.26"W, 2426 m, 4 January 2012, M. S. Samain et al. 2012-010 ( GENT!, MEXU!) [sterile]; loc. cit., 15°6'22.28"N, 92°6'11.11"W, 2423 m, 5 January 2012, M. S. Samain et al. 2012-011 ( GENT!, MEXU!) [sterile], M. S. Samain et al. 2012-012 ( GENT!, MEXU!) [sterile] .

Conservation: ―Critically Endangered; known from one population with adult flowering and juvenile runner shoots on the Volcano Tacaná on the border of Mexico and Guatemala, and five sterile, mostly juvenile collections by Julian Steyermark from Guatemala, none of them recent. Monitoring of remaining populations in Guatemala would be important for evaluation of the conservation status of H. steyermarkii in that country. On the Mexican side of the volcano ascending from the village of Chiquihuite, several flowering individuals have been observed, although only one functionally male individual could be sampled up to now, as a consequence of the quite inaccessible extremely steep slopes. There are many runner shoots on this locality, showing that this population most probably reproduces vegetatively. This area is located at approximately 5–6 km in straight line from the type locality on the Guatemalan side which could not yet be visited. The Mexican (sub)population is suffering as a consequence of habitat destruction and land use change, such as floriculture of Zantedeschia aethiopica (‘alcatraz’) and Hydrangea macrophylla cultivars.

Figures

FIGURE 2. Field pictures. A–B, Hydrangea albostellata, C–D, Hydrangea steyermarkii (M.S. Samain et al. 2012-010). A. Branch with one mature green inflorescence with old male flowers and inflorescence axes with the basal lignified parts of inflorescences of previous years (M.S. Samain et al. 2012-005). B. Abaxial leaf side with dense pubescence consisting of whitish stellate hairs, note the typical spoon-shape and broadly revolute margin (M.S. Samain & E. Martínez S. 2012-090). C. Young branch, many-ribbed, with typical brownish-reddish cortex which contracts and forms corchy patches. D. Abaxial side of young leaf with whitish stellate indument, the leaf surface typically red-brown, the margin crenate with the marked bright green glandular teeth.

FIGURE 3. SEM pictures of flowers of Hydrangea albostellata (A–D; A, C, M.S. Samain et al. 2012-023. B, D–E: M.S. Samain & E. Martínez S. 2012-088) and Hydrangea steyermarkii (E–F, M.S. Samain et al. 2012-078). A. Central parts of marginal female flower, with two large pistils and 3 small stamens visible. B. Flower bud of male flower; note the campanulate hypanthium and the valvate petals. C. Mature fruit opened between the pistils to release the seeds. D. Male flower; note the extreme difference in size between the long stamens and the diminute pistils. E. Lateral view of male flower. F. Apical view of male flower.

FIGURE 5. Hydrangea steyermarkii. A. Habitus of branch with inflorescences. B. Functionally male flower with 8 fertile stamens and 2 reduced pistils. C. Maturing capsule, fertile stigmas still visible, seeds are released through the opening between the 2 pistils. D. Inflorescence branch with inflorescence bud, inflorescence bracts and leaf pair visible. E. Detail of inflorescence branch with stellate indument. Drawn by Ramiro Cruz Durán from the specimen M.S. Samain et al. 2012-078 (MEXU; A, B, D, E), and from the holotype J.A. Steyermark 36044 (F; C).