Pleroma (plant)

Species of Pleroma are subshrubs, shrubs or trees. Their leaves are almost always opposite and petiolate, rarely sessile. The inflorescence is a terminal panicle or some modification of one. The flowers are perigynous with a bell- or urn-shaped hypanthium (base of the flower), usually externally covered with short, soft hairs (pubescent). There are usually five petals (sometimes four), purple to lilac, rarely white. The flowers have ten stamens (sometimes eight), often of two distinct sizes, with purple or pink anthers. The connective at the base of an anther is modified into a ventral bilobed appendage. The numerous seeds are contained in a dry semiwoody capsule and are spiral in shape, possibly elongated.[3]

The genus Pleroma was established by David Don in 1823.[1] He derived the name from Ancient Greek πλήρωμα, pleroma, meaning 'fullness', referring to the way the seeds filled the capsule.[4] Although Don used the genus name as a feminine noun, giving specific epithets feminine endings,[4] the Greek word is neuter, and subsequent authors have used neuter endings (e.g. Pleroma heteromallum rather than Don's Pleroma heteromalla).[3]

In 1885, in his treatment for Flora brasiliensis, Alfred Cogniaux used a broad concept of the genus Tibouchina, transferring into it species at that time placed in Pleroma and other genera. This broad concept was generally adopted subsequently, and around 470 taxa were at one time or another assigned to Tibouchina.[3] A phylogenetic analysis in 2013 based on molecular data (2 plastid and 1 nuclear regions) determined that the broad circumscription of Tibouchina was paraphyletic. Four major clades were resolved within the genus which were supported by morphological, molecular and geographic evidence.[5] A further molecular phylogenetic study in 2019 used the same molecular markers but included more species. It reached the same conclusion: the original broadly circumscribed Tibouchina consisted of four monophyletic clades. The authors proposed a split into four genera: a more narrowly circumscribed Tibouchina, two re-established genera Pleroma and Chaetogastra, and a new genus, Andesanthus. The part of their maximum likelihood cladogram which includes former Tibouchina species is as follows,[3] using their genus names and with shading added to show the original broadly circumscribed Tibouchina s.l. (The relationship between Chaetogastra and the genus Brachyotum differed between analyses.)

Pleroma is shown to be sister to Tibouchina.[3]

Pleroma species are mostly native to eastern Brazil in the Atlantic Forest and Cerrado biomes, more rarely in the Caatinga.[3] A few species reach other parts of South America and the Caribbean (Bolivia, Colombia, Ecuador, French Guiana, the Leeward Islands, Peru, Puerto Rico and Venezuela).[3][2] They are found in forests and forest margins, river banks, high altitude grasslands, rocky outcrops and restingas, from sea level up to an elevation of 2,650 m.[3]