The Neotropical genus Rudgea includes at least 150 species of shrubs and small to occasionallyl mid-canopy trees found widely in the New World tropics, in seasonal to moist and wet tropical forests and savannas, from low to high elevations. The genus is distinguished by its glandular stipules, which are varied in form: laminar with the margin laciniate and its segments gland-tipped, tubular and truncate with with a medial group of glands on each interpetiolar side, or laminar to tubular with a medial appendage of some sort with glands on the sheath margins and/or the appendages. Zappi (2003) detailed the variation in stipule form, and characterized several informal species groups that can be recognized by their stipules. The inflorescences are terminal and sometimes tardily displaced to pseudoaxillary, or occasionally these are axillary (Rudgea axilliflora, Rudgea quisquilliaei Torres-Leite et al., 2016). The flowers are 4--5(-8)-merous, distylous, and generally white and presumeably pollinated by insects. The corolla lobes are valvate in bud, and often bear ornate appendages. The ovary is 2-locular, with 1 basal ovule in each locule. The fruits are drupaceous and range from white to yellow, orange, red, or sometimes black, but they are not not blue or purple. The pyrenes are generally hemispherical (planoconvex), and contain 1 seed. The leaves of many species have well developed crypt-type or tuft-type domatia. The stems are generally developed and branching, but at least one or a few species from Brazil do have a trash-bucket habit with monocaulous stems and subsessile leaves that accumulate detritus (Rudgea macrophylla, Rudgea quisquilliae).
Rudgea is found in a notably wide range of habitats, from wet forest at low to montane elevations to Altantic coastal forest, semideciduous forest, cerrado, gallery forest, both flooded and non-flooded Amazonian forests, campo rupestre, and savannas, and has a similarly wide range of morphological variation. This genus is well represented in many areas, and has separated centers of species diversity in eastern Brazil, in the Guianas, in southern Central America, and and on the eastern slopes of the Andes. Rudgea cornifolia is the most widespread and commonly collected species. Rudgea viburnoides is common and commonly collected in much of Brazil and Bolivia, and Rudgea jasminoides has a nogably wide distribution from eastern Brazil to Argentina and Paraguay..
Rudgea is similar to Psychotria, Carapichea, Eumachia, Notopleura, and Palicourea, and has been confused with all of these at times (Taylor et al., 2015; Taylor & Bruniera, 2018). This confusion has been due in part to the separation of Rudgea by characters that are not unique to this genus, and in part to an incomplete understanding of the variation within all of these genera. In particular, Rudgea has been separated and circumscribed based on having glandular stipules, but further study now shows that glandular stipules of some form are also found in most of these other genera. Rudgea can be separated from these genera by a combination of stipule features: the presence of glands of some type, and a form that is not bilobed. The functional separation of Rudgea from these other genera is sometimes problematic, however, because the glands or colleters on the stipules of Rudgea are often caducous, and in some species they are only present on the apical node at a certain developmental stage. Carapichea generally lacks glandular stipules, although the separation of Carapichea ipecacuanha is problematic because this one species has laciniate laminar stipules with tips that may be glandular when young; Carapichea also generally has flowers that are subsessile or only very shortly pedicellate in groups that are enclosed by well developed bracts, while this arrangement is uncommon in Rudgea and generally associated with stipules of a different form. Eumachia sometimes has glandular stipules, but can generally be separated by the glands being situated at the tips of 1 or 2 slender or acicular lobes, and stipules that become indurated with age. Notopleura also has glandular stipules, often with a fleshy medial appendage, but can be separated by either its epiphytic habit, or is growth form as a fleshy monocaulous plant with regularly pseudoaxillary inflorescences (that is, the inflorescences are borne in one axil of each node along the stem, rather than in both axils as in Rudgea). Palicourea can be separated by its stipules that are bilobed to some degree, and sometimes also by its purple or blue fruits (Bruniera, 2015; Taylor et al., 2015). Rudgea was confused with Psychotria due to a general, complicated confusion over the identity of that genus in the Neotropics; Psychotria today can be separated by its caducous stipules that are not glandular but leave behind a persistent ring of trichomes on the stem.
Berger & Schinnerl (2019) and Berger et al. (2021) detailed some of the chemistry of secondary metabolites in this group, in Psychotria s. str. and the 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 Rudgea characterized by alstrostine metabolites.
The taxonomy of Rudgea has been studied only in regional floras so far, though a comprehensive review was started by Bruniera (2015) and is currently underway by her with several collaborators (Bruniera et al., 2015, in prep.; Torres-Leite et al., 2016). Regional floristic treatments have been published by Zappi (2003, 2006), Zappi & Steyermark (in Taylor et al., 2004), and Taylor (in Lorence & Taylor, 2012), Several groups of species can be separated within Rudgea based on morphological features, in particular stipule form (Zappi, 2003; Taylor & Bruniera, 2018), but more study is needed to understand the systematics of this genus.
Author: C.M. Taylor and Carla Poleselli Bruniera
The content of this web page was last revised on 19 Jan 2024
Taylor web page: http://www.mobot.org/MOBOT/Research/curators/taylor.shtml