The Tribe Henriquezieae includes 3 distinctive, morphologically unusual genera of the Amazon basin with about 22 species. These genera generally share a shrub or tree habit, usually resinous tissues that lack raphides, fused calyptrate stipules that are variously caducous or split into lobes, opposite or whorled leaves; terminal cymose inflorescences; relatively large, showy, (4)5(6)-merous, homostylous flowers; zygomorphic corollas with imbricate aestivation; stamens that are inserted at different levels on the corolla with filaments of different lengths; well developed, distinctive woody, loculicidal capsules; and relatively large, flattened seeds that lack or nearly lack endosperm. The pubescence of both vegetative and reproductive structures frequently consists of two layers, with the trichomes of the lower layer generally shorter and more appressed than those of the upper layer. Dávila (2016) described the resinous stem exudate as red in life in most of th4e species. The capsules are ellipsoid to suborbicular in outline, and flattened perpendicularly to the septum.
These three genera were treated together and illustrated by Bremekamp (1957), Rogers (1984), Dávila (2016), and Taylor et al. (2004). These genera characteristically grow in nutrient-poor, often poorly drained soils. Henriquezia and Platycarpum are additionally distinctive in having 1 to several glands at the abaxial bases of the petiole, particularly waxy leaf cuticles, and semi-inferior ovaries and fruits. Gleasonia is distinctive in having the five calyx lobes enlarged into petaloid calycophylls on all the flowers in an inflorescence. With a little over a dozen species, Platycarpum is the largest genus of the tribe. Henriquezia and Platycarpum are additionally intriguing in each having one species in Guyana that is disjunct from the rest of the genus.
Henriquezieae was studied most recently by the talented Peruvian botanist and ecologist Dr. Nallarett Dávila (1980-2022), who unfortunately was not able to publish all of her dissertation research. She did extensive field work, annotated specimens, and kindly discussed her results as they developed (pers. comm.), and was able to publish some of her work (Dávila, 2016; Dávila & Kinoshita, 2016). Some of the taxonomic conclusions here incorporate the unpublished portion of her work.
The fruits and seeds of the Henriquezieae genera and their zygomorphic flowers are not similar to other Neotropical Rubiaceae. Superior or partially ovaries or fruits are found in a few other genera, notably Pagamea. The petiolar glands are unique to Henriquezia and Platycarpum, although the petiole bases of Gleasonia are notably broadened at the abaxial base. These two genera also have been reported to lack colleters (Cronquist, 1981), and Rogers (1984) did not analyze this statement in his morphology section but did in his taxonomic treatment describe colleters that are found in the stipules of Gleasonia but absent from the other two genera. Reduced endosperm is also found in some genera of Guettardeaee. Gleasonia is distinctive in part in its intrapetiolar stipule segments, a feature also found in some other Rubiaceae genera. Dávila diagnosed this tribe additionally by its maculate or lined corollas, but these are found in some other Rubiaceae (e.g., Sphinctanthus). See Rogers (1984) for a detailed comparative analysis of the morphology of these three genera.
The Henriquezieae has been circumscribed with these three genera by recent authors (Rogers, 1984; Robbrecht, 1988). This tribe was described with two genera, Heriquezia and Platycarpum, and then Gleasonia was considered to be closely to related to these by Cronquist (1981) and then formally added to Henriquezieae by Rogers (1984). The inclusion of Gleasonia in Rubiaceae has generally not been questioned, but the other two genera are so idiosyncratic morphologically they have been variously included in Bignoniaceae or separated in their own family, as Henriqueziaceae (Steyermark, 1952; Bremekamp, 1957, 1966; Verdcourt, 1958), and Gleasonia has been separated in its own subfamily of Rubiaceae (Bremekamp, 1957, 1966). Within Rubiaceae, Gleasonia has been variously included in a large tribe, the traditional Rondeletieae (Standley, 1931), or even separated as its own monogeneric subfamily (Bremekamp, 1966). Only one genus, Henriquezia, wwas included in the molecular analysses of Bremer & Eriksson (2009), who found this grouped with Sipaneeae and Posoquerieae. Subsquently Cortés-B. & Motley (2015) analyzed all three of these genera with molecular systematic data, and found some different affinities of Gleasonia among diffferent data sets but concluded by recognizing Henriquezieae with these three genera.
Author: C.M. Taylor The content of this web page was last revised on 29 December 2023.
Taylor web page: http://www.mobot.org/MOBOT/Research/curators/taylor.shtml