Rinorea uxpanapana T.Wendt

  • Authority

    Hekking, W. H. A. 1988. violaceae Part l—Rinorea and Rinoreocarpus. Fl. Neotrop. Monogr. 46: i-ii, 1-208. (Published by NYBG Press)

  • Family

    Violaceae

  • Scientific Name

    Rinorea uxpanapana T.Wendt

  • Type

    Type. Mexico. Veracruz: Mun. Minatitlán, 13.7 km E of La Laguna, terrace of Uxpanapa, 17°20'N, 94°23'E, 130 m, 28 Apr 1982 (fl), Wendt et al. 3907 (holotype, MEXU; isotype, U; isotypes not seen: BM, CAS, CHAPA, COL, CSAT, ENCB, F, HH, INIF, MO, NY, TEX, US, XAL).

  • Description

    Species Description - Treelet 4 m tall. Branchlets glabrous, possessing two kinds of leaves: laminar leaves, alternate to subopposite in the apical part of the branchlets, and scale-like leaves in the basal part of the branchlets. Laminar leaves petiolate, more or less soon deciduous; petioles articulate at the base, 2-6 mm long, glabrous beneath, puberulous above; stipules subpersistent, narrowly ovate, oblique at the base, 1.5-2.5 x 0.5-1 mm, scarious, costate, glabrous, margin ciliate at the base, apex (sub)obtuse, mucronulate; lamina, narrowly elliptic, acuminate, 4.5-15 x 1.5-5.5 cm, papery; lamina, costa and lateral veins glabrous on both sides; domatia wanting; lateral veins 5-7(-8) pairs (acumen excluded); tertiary venation reticulate; base rounded to cuneate; margin subcrenate, mucronulate; acumen 1-1.5 cm long, apex (sub)obtuse to (sub)acute, mucronulate. Scale-like leaves subsessile, distinctly more costate than its two subpersistent stipules; stipules as those of laminar leaves; lamina of scale-like leaves minute, ovate, acuminate, 1.5-2 x 0.5-1(-1.25) mm, scarious, sparsely pilose to glabrescent, distinctly costate, margin entire, irregularly ciliolate, apex subobtuse mucronulate. Inflorescences axillary, lateral or subterminal, 1-3 fasciculate, cymose; cymules contracted, subsessile, containing 1-3 flowers; common peduncle 0-0.25 mm long, glabrous; pedicels 4-7 mm long, articulate at the base, glabrous; bracts and bractlets close together at the base, widely ovate, (sub)obtuse, mucronulate, scarious, costate, margin fimbriate and ciliolate; bracts ca. 1 x 1-1.25 mm; bractlets ca. 0.5 x ca. 0.6 mm. Flower buds conical, obtuse. Flowers creamy to pale yellow. Sepals subequal, deltoid to ovate, 1-1.5 x 0.6-1.2 mm, herbaceous, glabrous, costate, margin scarious, fimbriate and cili(ol)ate, apex acute to obtuse, obscurely mucronulate. Petals elliptic to ovate, 2.75-3.75 x 1.25-2 mm, herbaceous, carnose along the median part, glabrous, margin scarious, not ciliolate, apex obtuse to rounded. Stamens ca. 2.5 mm long; filaments 0.2 x 0.30.4 mm, fused to a sinuate tube 0.2-0.3 mm high; dorsal glands ca. 0.3 mm long, carnose, glabrous, fused with the tube; anthers ellipsoid, ca. 0.75 x ca. 0.25 mm, glabrous, apex rounded, unappendaged; connective outside, ovate, subobtuse, 0.20.4 mm long, glabrous; connective scales lateral as well as apical, ovate, 2-2.25 x 0.6-0.75 mm, scarious, orange-brown, at the base uncolored and transparent, margin subentire, apex suberose and obtuse. Ovary subglobose, ca. 0.75 mm in diam.; ovules one per placenta. Style filiform, erect to slightly curved near the apex, exceeding the stamens by 0.25-0.75 mm, completely glabrous; stigma 3-lobulate, erect to slightly deflexed to the anterior petal. Fruits unknown.

  • Discussion

    Annual rainfall in this area is ca. 4000 mm, but there is also a pronounced dry season of ca. 2 months; climatic drought in the area is further enhanced by the karstic limestone habitats on which Rinorea uxpanapana grows. Nevertheless, these relatively dry conditions are apparently not unfavorable, since such species as R. deflexiflora, R. guatemalensis and R. hummelii grow together with this species (Wendt, 1984).

    Rinorea uxpanapana differs from all other neotropical species of Rinorea by the combination of the following characters: (1) the occurrence of two different kinds of leaves: (a) laminar leaves with distinct petioles and laminae and (b) subpersistent, scale-like leaves; (2) stipules also subpersistent, scarious and oblique at the base, in habit similar to the scale-like leaves; (3) petioles of laminar leaves articulate at the base; (4) minute cymose inflorescences 1-3 fasciculate and subglomerulate in the axils of both kinds of leaves; cymules (nearly) without peduncle and provided with only 1-3 flowers; (5) basal parts of ‘pedicels’ reduced (as in Subgroup Ilc.2. Viridifolia), whereas the apical parts are elongated; (6) petals subequal, tending slightly to zygomorphy by anterior petals being slightly larger than the posterior ones; (7) filaments and dorsal glands fused to a filamental tube (as in R. ramiziana and in the Subgroups IIa.3. Rinorea and Ile. 10. Racemosa); (8) ovary glabrous with ovules one per placenta (as in Supergroup I. Apiculata); and (9) stigma trilobed, which is exceptional in Rinorea.

    The slight zygomorphy of the flowers of Rinorea uxpanapana suggests a close relationship to some Rinorea species of the Old World as well as to Hybanthus mexicanus (syn.: Alsodeia (=Rinorea) parvifolia Watson), belonging to the tribe Violeae; there also exists a remote relationship to the genus Orthion which also belongs to the Violeae; all these taxa mentioned are restricted to Central America. The occurrence of the slightly zygomorphic flower character in both tribes, Rinoreeae as well as Violeae, the distinction between them has been become less sharp than presumed before. Rinorea uxpanapana is the only neotropical species with minute cymose inflorescences, in contrast to the paleotropical situation, where more species occur with cymose inflorescences. A reduced subsessile cymose inflorescence, as in R. uxpanapana and in other, paleotropical, species, can be considered as the stage most derived from the thyrsoid, which has been postulated as the basic inflorescence structure in Rinorea. The reduction to this short-peduncled cymose inflorescence can be explained by an acrotonic suppression of the central axis of a previously existing thyrsoid inflorescence (see Morphology). Since the Mexican R. uxpana-pana seems to be more related to paleotropical than to neotropical species, a common origin during the late Cretaceous and the Paleogene, when exchange of genetic material between Africa and tropical South America was still possible, is most likely. During the Pliocene, however, both continents became so far separated from each other, that the distance between them more and more became a limiting factor for genetic exchange. Therefore, the isolated population of R. uxpanapana in southern Mexico may be considered as a relict, probably originating from a common African-South American stock, from which ancestors of related species of Hybanthus and Orthion probably also originated. From tropical South America it possibly migrated via the Colombian area to Central America, synchronously with extinction on the South American mainland. Such a migration must have started before the high uplift of the Cordilleras during the Pliocene. For this presumed migration to Central America, two geological periods can be considered: a) a more recent period in the Pliocene, during the creation of the Panama land bridge, ±5.7 my B.P. or b) much earlier during the late Cretaceous and Paleogene via the Proto Greater Antilles Arch, which was situated far SW of the present position, i.e., before it was swept through the widening gap between North and South America (Coney, 1982). Because of the isolated taxonomic position of R. uxpanapana as well as by its presumed closer relationship with some paleotropical species, the period of late Cretaceous and Paleogene is most likely. Closely related species of Orthion and Hybanthus, with slightly zygomorphic flowers, and also predominantly occurring in Central America, probably originated from the same common or closely related ancestral stock as did Rinorea uxpanapana. It is striking that the flowers of R. uxpanapana are also similar to those of the subgroups ‘Rinorea’ and ‘Racemosa.’ However, it is not excluded that Rinorea uxpanapana must be transferred to Hybanthus Jacq. subgenus Hybanthus (=Euhybanthus sensu G. K. Schulze, 1936) after a future revision of neotropical Hybanthus and after collection of additional, especially fruiting, material of Rinorea uxpanapana.

  • Distribution

    Known only from the type collection in Zona Uxpanapa, Los Tuxtlas (forest refuge) in southern Vera Cruz on the Isthmus of Tehuantepec, SE Mexico. Altitude ca. 125 m. The type specimen has been collected in a medium high deciduous forest, characterized by an occurrence of Bursera simaruba, Spondias radlkoferi, etc.

    Mexico North America| Veracruz Mexico North America|