Notopleura (Benth. & Hook.f.) Bremek. is a Neotropical group that includes about 110 species of fleshy, suffrutescent plants and epiphytes distributed widely in the New World tropics. Notopleura plants are found in moist to wet tropical forests, from low to high elevations. A few species are branched epiphytes with terminal inflorescences, but most of the species are rather unusual terrestrial plants with regularly pseudoaxillary inflorescences. These terresrial plants are quite fleshy and usually unbranched, and generally about 1 m tall. Notopleura is characterized by this habit, its stipules of varied and unusual form, cymose to paniculiform inflorescences, rather small, distylous, usually 5-merous flowers, corollas with the lobes valvate in bud, 2-locular ovaries with 1 basal ovule in each locule, drupaceous fruits of vairous colors with two pyrenes, and generally hemispherical (planoconvex) pyrenes each with a single seed. The leaves lack domatia. The inflorescences of the terrestrial plants are characteristically pseudoaxillary in the sense of Robbrecht (1988): this position results from a developmentally terminal inflorescence produced on a sympodial stem, so the inflorescences are regularly borne along the stems with one inflorescence borne at each node of the decussate leaves and those of successive nodes borne on alternating sides of the stem. The flowers are white, relatively small, and presumeably pollinated by insects. The corollas are generally white, and frequently have unusual, often prolonged appendages on the corolla lobes; in a few species, the corollas are orange or pink. The carnose fruits are white, orange, red, or sometimes black, and presumably dispersed by birds.
Berger & Schinnerl (2019) and Berger et al. (2021) detailed some of the chemistry of secondary metabolites in this group, in Psychotria s. str., Palicourea s. lat., and other genera of Palicoureeae, and found chemical differences between Psychotria, which lacks alkaloids and contains tannins, and the genera of Palicoureeae, with some characteristic types of alkaloids and without tannins.Within this pattern, they found Notopleura characterized by quinone metabolites.
The stipules of Notopleura vary widely in form in the genus, and are generally glandular; the basic form as well as the range of different forms in the stipules of Notopleura are similar to the stipules of Rudgea. The stipules of Notopleura are generally persistent or tardily dehiscent, except their glands and sometimes their appendages are deciduous. The stipules of the epiphytic Notopleura species are generally fused around the stem in to a truncate tube with a medial appendage or group of glands on each interpetiolar side. The stipules of the terrestrial species are variously fused around the stem to nearly interpetiolar (here called laminar), with the interpetiolar portion glandular and rounded to triangular or shortly bilobed, and often appendaged. The stipule appendages are generally inserted medially or near the base, and range from a narrow succulent projection to a broad laminar structure that is larger than the basal part of the sheath. These sheaths and projections usually have deciduous glands of some form on the margins or the tips of the projections. The stipule form appears to be distinctive for an individual species, but these often are very succulent and are not preserved well on dried specimens. The function of these ornamented, glandular stipules is not known, and field observations will be needed to understand the role of the stipules in the ecology of these species. Lachenaud & Delprete (2022) also documented apparent dimorphism in the stipules of Notopleura tapajozensis, in which the sheath portion of vegetative stipujles is reduced to a line on reproductive nodes. They regarded this as a newly reported character in Rubiaceae, but the stipules subtending the peduncle in Palicoureeae are typically reduced in various ways and irreigularly developed, so this perhaps represents an extreme level of reduction rather than a different morphology.
The species of Notopleura were long included by most authors in Psychotria, and most recently in Psychotria Subg. Heteropsychotria Steyerm. Then, consideration of morphological (Taylor, 1996, 2001) and molecular (Andersson & Rova, 1999; Nepokroeff, 1997; Nepokroeff et al., 1999) characters found that Neotropical Psychotria was polyphyletic and the species of Notopleura represent a separate lineage that is more closely related to Rudgea, Geophila, and Palicourea than to Psychotria. Bremekamp first separated Notopleura in his study of Psychotria sensu lato in Suriname, and included two species in this genus. In that work he separated from Psychotria a dozen or so small genera that were immediately synonymized with Psychotria, Palicourea, and Rudgea by contemporary and later authors, who followed the general consensus and, among other decisions, continued to include Notopleura in Psychotria. Then, based on those late-20th-century studies Taylor (2001) separated Notopleura from Psychotria with a synoptic treatment of the species identified as belonging to that group.
Taylor (2001) separated two subgenera of Notopleura, with the terrestrial species with pseudoaxillary inflorescences included in Notopleura subg. Notopleura and the epiphytic species with terminal inflorescences included in Notopleura subg. Viscagoga. Both of these subgenera are found generally throughout the range of the genus. The epiphytic species are separated by rather subtle, largely vegetative features, and probably deserve re-evaluation using molecular characters and also field observations to understand the range of varation within a population. The terrestrial plants were long included in a few widespread, morphologically widely variable species, and most of its plants were treated as Psychotria macrophylla (e.g., Standley, 1938, Steyermark, 1972). Taylor (2001) used details of features such as stipule form, inflorescence arrangement, bract development, corolla size, and fruit color to separate those plants into a number of species, and then (Taylor, 2003) described additional species. Subsequently some species were added to and transferred from Notopleura by Taylor et al. (2004), and additional species were discovered.
More recently, Carapichea in the Guianas was reviewed in more detail with field study and additonal specimens by Lachenaud & Delprete (2022). They revised the circumscription of the genus by transferring three species to Notopleura, based on additional characters they observed and similarities to Notopleura tapajozensis and Notopleura aneurophylla. These three transferred species, treated previously as Carapichea altsonii, Carapichea nivea, and Carapichea sandwithiana, were poorly known to previous authors. and noted to share features with Notopleura but excluded from that genus based on their terminal inflorescences. Lachenaud & Delprete concluded that these are better placed in Notopleura subg. Notopleura and apparently related to Notopleura tapajozensis. They noted that an unpublished molecular study had found Notopleura tapajozensis in a basal position within that genus. All of these species are distinctive within Notopleura in aspect and several features and tmay deserve further systematic evaluation.
The terrestrial species of Notopleura are similar to Hoffmannia, which often has similar stipules with a succulent medial appendage; Hoffmannia can be separated by its inflorescences that are axillary, so they are produced in both axils of a stem node rather than just on one side, along with its corolla lobes that are imbricated in bud and its baccate fruits with numerous small seeds. Notopleura is also similar to Rudgea, which can be separated by its terrestrial, branched habit that is not particularly succulent and its generally terminal inflorescences. Psychotria can be separated from Notopleura by its generally caducous stipules that leave a line of persistent trichomes on the stem after they fall, their leaves often with domatia, and their generally terminal inflorescences. Eumachia can be separated from Notopleura by its stipules that usually become yellow and hardened with age and inflorescences that are terminal or pseudoaxillary but then also borne terminally. Palicourea can be separated from Notopleura by its bilobed stipules that lack medial appendages and terminal inflorescences, which may become pseudoaxillary as the stem develops but are not regularly borne on alternate side of the stem.
Author: C.M. Taylor. The content of this web page was last revised on 29 January 2024.
Taylor web page: http://www.mobot.org/MOBOT/Research/curators/taylor.shtml