Abstract
Hydrangea section Cornidia, currently consisting of 19 accepted taxa, occurs from Mexico to Chile and Argentina, with one species in southeast Asia. Its representatives are root-climbing lianas which may grow up to 60 m high in the tree canopy of temperate to (sub)tropical forests. Our extensive field work throughout its distribution area, study of herbarium specimens and ongoing molecular studies have resulted in the discovery of species new to science, as well as new insights into the circumscription of many taxa. We here present amended descriptions for seven Hydrangea species of Central and South America and discuss the taxonomical situation of two Colombian Hydrangeas, including an identification key, illustrations, and distribution maps. Field work was carried out in Costa Rica, Panama, Ecuador and Peru, including exploration in areas where the genus had not been collected before. These specimens and observations were complemented with the study of specimens of 41 herbaria of North, Central and South America, as well as Europe. Detailed morphological studies of all species were carried out, based on living plants in their natural habitat, as well as on dried specimens from our own collections and all available herbarium material. Type material was studied in detail for all species concerned. Based on an extensive number of morphological characters, combined with distribution patterns, phenological differences and ecological preferences, including molecular data in most cases, Hydrangea peruviana and H. oerstedii are clearly distinct taxa, as well as the other seven species mentioned here, which had been synonymized with either of these two species. The present study results in the recognition of 26 species in section Cornidia and exemplifies the urgent need for profound taxonomic studies in plants, as in many families we do not dispose of well-circumscribed units for conservation to mitigate the already occurring unprecedented loss of biodiversity.
Highlights
The relatively poorly known Hydrangea L. section Cornidia Ruiz & Pav. consists of 19 currently accepted taxa (18 species and one variety) and a yet undefined number of species new to science and taxa that have been erroneously synonymized
Our field observations were complemented with a detailed study of relevant herbarium specimens of 41 herbaria in Europe, North, Central and South America (A, AAU, AMAZ, B, BM, BR, C, CAS, COL, Córdoba 327 (CR), DUKE, E, F, G, Ghent University (GENT), GB, GH, HOXA, HUA, IEB, INB ( CR), K, LOJA, MA, MEXU, MICH, Mori & Bolten 7248 (MO), MOL, MPU, NY, P, PMA, QCA, QCNE, QPLS, UC, UCH, UPS, US, USM, and WU; acronyms according to Thiers, continuously updated), most of them loaned, few in high resolution on JSTOR Global Plants
There are other taxa with similar colors but these have never been synonymized with the two abovementioned species, South American herbarium specimens of these taxa may be identified as H. peruviana
Summary
The relatively poorly known Hydrangea L. section Cornidia Ruiz & Pav. consists of 19 currently accepted taxa (18 species and one variety) and a yet undefined number of species new to science and taxa that have been erroneously synonymized. Hydrangea section Cornidia (hereafter shortened as Cornidia) is monophyletic, including the single Asian species (Samain et al 2010; Granados Mendoza et al 2013a, b, 2015; De Smet et al 2015), and is sister to the section Calyptranthe Maxim., consisting of Asian climbing species (De Smet et al 2015). Both clades together are sister to the section Asperae (Rehder) Y.De Smet & Samain, encompassing Asian shrubby species (De Smet et al 2015). As already noted by Samain et al (2019), we do not follow the nomenclatural changes proposed by Ohba and Akiyama (2016), who suggest recognition of Cornidia as a segregate genus within tribe Hydrangeeae, together with most of the other sections published by De Smet et al (2015), as they do not take into account the evolutionary context in which the new classification of the tribe Hydrangeeae was presented
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