Palicourea sect. Axillares includes 14 species from tropical Central America, South America, and the Anilles. It was diagnosed by Taylor (2021) within Palicourea by the combination of its stipules that are laminar, relatively well developed, and bilobed and enclose the inflorescences variously shortly to markedly; inflorescences that have ca. 9 or more sessile to subsessile flowers and are pseudoaxillary or sometimes also borne at the stem apex, are capitate or sometimes have axes that expand tardily, and have well developed bracts but are not enclosed by enlarged involucral bracts; salverform corollas with the lobes smooth abaxially, and a cylindrical tube that is not swollen at the bottom and is pubescent internally in its top portion; blue-black to bright blue fruits; and hemispherical pyrenes that are abaxially ridged and adaxially plane with a median longitudinal furrow. Palicourea sect. Axillares is additionally characterized by its often slender, shrubby to small tree habit, medium-sized petiolate leaves that often have a distinctive silvery or pale abaxial epidermis, bracts that are often cucullate and/or fibrous, calyx lobes that are usually ciliate on the margins, and habitat in wet, usually premontane to montane vegetation. Palicourea axillaris is the most widespread, commonly collected, and morphologically variable species in the group.
Here (Taylor, 2021), Palicourea sect Axillares is circumscribed following Steyermark (1972), with the addition of some species discovered since his work. Palicourea axillaris, however, is circumcscribed somewhat differently from Steyermark, and no infraspecific taxa are recognized. One species included here, Palicourea pastazana, is unusual in Palicourea in its inflorescences that are borne at stem nodes variously in one (i.e., pseudoaxillary) or both (i.e., axillary) axils, with both positions sometimes found on one plant (e.g., Clark et al. 8926, MO). The developmental pattern of these inflorescences is not entirely clear, but certainly shows some of the morphological and developmental plasticity in Palicourea.
Two species, Palicourea pastazana and Palicourea santanderiana, have the diagnostic features of Palicourea sect. Axillares, but also share some characters with Palicourea sect. Montanae ser. 4 subser. f (i.e., the Palicourea pilosa Group; Taylor, 2019) and may have relationships instead in that group. Two other species included her in Palicourea sect. Axillares, Palicourea quibdoana and Palicourea pseudaxillaris, agree with the general characters of this section except for their bract form, which is not shared with any other Palicourea species and thus not indicative of another relationship. Two species included in Palicourea sect. Chocoanae (Taylor, 2017), Palicourea mistratoana and Palicourea shuar, share many of the features of Palicourea sect. Axillares but differ in thier terminal, pedunculate, branched inflorescences with flattened bracts; they may be found to belong instead to Palicourea sect. Axillares, which will expand the variation in inflorescence form within this group.
Borhidi (2017) first recgnized Palicourea sect. Axillares at the sectional level, with a revised circumscription from Steyermark's Psychotria ser. Axillares, a limited morphological characterization based on naviculiform or cucullate bracts, and no discussion. The changes that Borhidi made to Steyermark's circumscription of this group are not accepted here. Borhidi excluded from this section two of Steyermark's species, Psychotria liogieri and Psychotria rosacea, and also added two species that Steyermark placed in other groups, Psychotria campylopoda and Psychotria schlimii. The two species he excluded from this group have its characters (and in fact are so similar to Palicourea axillares that immature plants can be difficult to separate),m and these are again included in this section here. The two species Borhidi added to his section lack its characters and are biogeographically and ecologically discordant, and are here included in other Palicourea groups. Palicourea campylopoda is a species of seasonal scrub vegetation on nutrient-poor soils in northeastern South America, and differs from Palicourea sect. Axillares in its three-flowered pedunculate inflorescences that are terminal on the main and/or short lateral stems, small stipules with a truncate sheath and two narrowly triangular acute lobes, and pyrenes that are smooth abaxially; Palicourea campylopoda is not here classified within this genus pending further study. The other species, Palicourea schlimii from premontane and montane vegetation in eastern Colombia, is not closely similar to any other Palicourea species, as noted by Steyermark (1972). It differs from Palicourea sect. Axillares in small stipules with a truncate sheath and narrowly triangular lobes, flowers borne in three-flowered heads or dichasial groups with only a few small bracts, and pyrenes that are abaxially smooth. Palicourea schlimii agrees morphologically with Palicourea sect. Psychotrioides C. M. Taylor and was included there by Taylor (2021).
The content of this web page was last revised on 20 June 2021.
Taylor web page: http://www.mobot.org/MOBOT/Research/curators/taylor.shtml