Gleasonia

  • Authority

    Rogers, George K. 1984. Gleasonia, Henriquezia, and Platycarpum (Rubiaceae). Fl. Neotrop. Monogr. 39: 1-135. (Published by NYBG Press)

  • Family

    Rubiaceae

  • Scientific Name

    Gleasonia Standl.

  • Type

    Type species. Gleasonia duidana Standley. The name was chosen in honor of Dr. H. A. Gleason.

  • Description

    Genus Description - Shrubs or small trees. Young stems striate or ribbed, glabrous or with pale hairs. Stipules arranged with single pointed lobe centered over each petiole, the lobes usually over 1 cm long, provided adaxially at base with numerous dark-colored colleters. Leaves decussate; lamina elliptic to oblanceolate, rounded to acute at apex, rounded to cuneate at base, the margins mostly revolute, adaxially glabrous or sparsely pubescent, abaxially with pubescence usually concentrated on large veins. Inflorescence a large complex cyme with the main axis not strongly developed; distal bracts linear to narrowly lanceolate. Flowers large and showy; calyx lobes 5, unequal, to 10 x 2.5 cm, white with reddish base, spatulate or differentiated into claw and limb; corolla 2-5 cm long, pink to violet, sometimes zygomorphic, externally densely pale-hispid, internally tomentose to villous; corolla lobes spreading, usually oblong to broadly deltoid, acute to rounded at apex; stamens tending to be unequal; filaments inserted near middle of corolla tube; style usually tomentose. Capsule ca. 1-3 x 1.5-3.5 cm, 0.5-2.0 cm thick, brown (dry). Seeds 2-many per locule, borne nearly vertically, flat, rounded, papillose.

  • Discussion

    Species of Gleasonia are recognizable by their actinomorphic or slightly zygomorphic, reddish corolla, which is shorter than its striking calyx of five, white, spatulate or pseudopetiolate lobes which are the most conspicuous elements of the cymose inflorescence. Unlike Henriquezia and Platycarpum, the stipules are arranged with a large lobe centered over each of the opposite petioles and are provided adaxially at the base with colleters.

    Taxonomic History of Gleasonia

    Standley (1931) tentatively assigned Gleasonia to the rubiaceous tribe Ron-deletieae, noting that because he had not seen fruits or seeds, “there is some question as to the tribal position of the tree.” Steyermark (1967, 1974) retained the genus in the Rondeletieae with which it shares imbricate or contorted aestivation of the corolla lobes, capsular fruits, pitted testa cells, an arborescent habit, and bilocular ovaries (tribal characters from Bremekamp, 1966 and Verdcourt, 1958). But Gleasonia is atypical for the tribe by having more or less vertically borne seeds which lack endosperm.

    Bremekamp (1957) emphasized the lack of endosperm, the embryo “with its large cotyledons and short axis,” and the large pollen as reasons for segregating Gleasonia into a new subfamily, the Gleasonioideae.

    All three genera share all of the characteristics mentioned above: those connecting Gleasonia to the Rondeletieae, those by which Gleasonia differs from the Rondeletieae, and those by which Gleasonia is odd in the Rubiaceae.

  • Distribution

    Four species distributed in the Guayana Highland of southeastern Venezuela, in the region of the upper Rio Negro of northern Brazil, and (G. cururuensis) near the upper Rio Tapajos, a southern tributary of the Amazon River in Pará, Brazil (Fig. 179).

    Venezuela South America| Brazil South America|