Henriquezia includes 3 species of shrubs and trees found in northeastern South America. This genus is characterized by its robust overall habit; stems with ample resin in a layer just below the outer surface; opposite or usually whorled, robuse, stiff-textured petiolate leaves without domatia; petioles that have 1-2 large round glands at the base; well developed stipules that are calyptrate in bud and then split into two interpetiolar segments; terminal, robust inflorescences with cymose axes; rather large, showy, 5-merous flowers; well developed calyx lobes; funnelform, white to red corollas with the lobes imbricated in bud; woody, large, loculicidal capsules that are semi-inferior and strongly laterally flattened; and relatively large, rounded, flattened seeds. The species are characteristically found along rivers, in nutrient poor sandy or sometimes silty soils. Henriquezia was studied in detail by Rogers (1984). Henriquezia nitida is the most widespread and commonly collected species.

The stem resin of Henriquezia was described by Dávila (2016) as red. The leaves are generally quite regularly elliptic with obtuse to rounded or sometimes shortly retuse and/or apiculate apices. The leaves often also have a notably waxy cuticle, which appears as a bloom on dried specimens. This wax as been described as deposited in papillae, and found predominantly on the lower surface except in Henriquezia jenmanii, where it is reported as primarily deposited on the upper surface (Rogers, 1984); the documentation of this is perhaps not entirely clear. The stipules are interpetiolar but distinctive in being split fully into two separate segments, and fused to the petioles on each side. The secondary inflorescence axes are variously paired or whorled, with at least the basalmost axes usually verticillate but the subsequent axes varied in arrangement or more often paired. Rogers (1984) noted that the flowers are 5-merous, except the calyx lobes variously may be 4 or 5 (Steyermark, 1952; Dávila. 2016). The calyx lobes of Henriquezia are well developed, white-flushed, and pubescent, but not expanded into calycophylls. The illustration of Henriquezia nitida presented by Taylor et al. (2004: 619, fig. 484) is generalized and may give the inaccurate impression that the ovary is superior. The corollas are showy and widely flared, and rather large (2-6 cm long).These are strikingly marked inside with red lines and spots. These corollas are also densely pubescent internally, and ihave yellow bearded pubescence. The capsules are flattened parallel to the septum. The ovary of the flower is inferior, but the fruit elongates in the upper part to become partially superior as it developed. 

Henriquezia includes 2 species that are found widely and sympatrically in the Rio Negro-Orinoco drainge, and one species (Henriquezia jenmanii) that is infrequently collected and disjunct in the lower Mazaruni and Essiquibo River drainge of northern Guyana. The species of Henriquezia are notable in their unusual morphological features, and notably variable in leaf size and shape, degree of development of the inflorescences, and size of the flowers, and have a complex taxonomic history. Different authors have viewed these plants and their morphological variation diffferently. Steyermark (1963) considered it taxonomically informative of distinct or diverging taxa, and recognized four species as well as several varieties of both Henriquezia nitida and Henriquezia verticillata. He separated these taxa based on details of leaf shape and size, number and degree of visibility of the leaf veins, length of the calyx lobes, and degree of persistence of the stipujles; most of the new varieties he recognized were documented by only a few specimens. Rogers (1984) reviewed addtional specmiens, and found many of Steyermark's taxa now linked by continuous variation. He recognized 3 species of Henriquezia and only three varieties, all in Henriquezia nitida. Dávila (2016) tested these classifications with yet more specmiens and field work, and concluded by recognizing 3 variable species of Henriquezia with no varieties. The extent of the variation oin these species is evident just wiithin Henriquezia jenmanii, which is known from perhaps fewer than a dozen specimens: this species was diagnosed by Rogers (1984) in part by its leaves that are "usually" acute to acuminate at the apex, and this feature is found on a number of the specimens but it is not present on the holotype and another K specimen, which have rounded to retuse leaf apices. 

The classification of Henriquezia has varied and has been problematic due to several of its unusual features, notably the semi-inferior ovary, apparently free stipules, and glands sugtending the petioles. The family classification of this genus was problematic for some time, and this genus was placed variously by itself and with Platycarpum in its own family, Henriqueziacae, and in Bignoniaceae. Bremekamp (1957, 1966) found the unusual (autoapomorphic) features to make inclusion in the Rubiaceae problematic, while Rogers (1984) and Cronquist (1981) found these to be idiosyncratic individual features that do not indicate its relationships while the other characters of this genus show it belongs to Rubiaceae. More recently, molecular data have found Henriquezia nested well within Rubiaceae (Cortés-B. & Motley, 2015). The separation between Henriquezia and Platycarpum also was not always completely clear, and some species described in one genus now are included in the other. The molecular analysis of Cortés-B. & Motley also found these two genera supported as separate. 

Author: C.M. Taylor The content of this web page was last revised on 27 December 2023.
Taylor web page: http://www.mobot.org/MOBOT/Research/curators/taylor.shtml

Humid, seasonal, lowland forest and scrub, generally along rivers and often on sand substrates, 50-200 m, Guayana region of northeastern South America (Brazil, Colombia, Guyana, Venezuela).

• Rogers, G. K. 1984. Gleasonia, Henriquezia, and Platycarpum (Rubiaceae). Fl. Neotrop. Monogr. 39: 1–135.
• Dávila, N. 2016. Phylogeny Taxonomy Henriquezieae 1–123.
• Steyermark, J. A. 1963. Rubiaceae In: B. Maguire & collaborators, The botany of the Guayana Highland—Part V. Mem. New York Bot. Gard. 10(5): 186–278.
• Cortés-Ballén, R. & T. J. Motley. 2015. Phylogeny of the Henriquezieae-Posoquerieae-Sipaneeae, a Guayanan-centered clade of Rubiaceae: implications for morphological evolution. Phytotaxa 206(1): 90–117.
• Steyermark, J. A. 1952. The genus Platycarpum (Rubiaceae). Amer. J. Bot. 39: 418–423.
• Bremekamp, C. E. B. 1957. On the position of Platycarpum Humb. et Bonpl., Henriquezia Spruce ex Bth. and Gleasonia Standl. Acta Bot. Neerl. 6(3): 351–377.
• Bremekamp, C. E. B. 1966. Remarks on the position, the delimitation and the subdivision of the Rubiaceae. Acta Bot. Neerl. 15: 1–33.
• Cronquist, A. J. 1981. Integr. System Classific. i–xviii, 1–1262. Columbia University Press, New York.