Abstract
Background: Hydrangea section Cornidia consists of 26 currently accepted species and a yet undefined number of new species and erroneously synonymized taxa. This clade consists of (sub)tropical lianas occurring from northern Mexico to southern Chile and Argentina, and one species from Southeast Asia. Currently, no molecular phylogenetic hypothesis is available that includes more than a few species of this section. Hence, a resolved and well-sampled molecular phylogenetic hypothesis may help to enforce taxonomic decisions. In this study, we present a phylogenetic framework based on sequences from two low copy nuclear genes from a comprehensive taxon sampling of H. section Cornidia and a selection of outgroups. Our phylogenetic reconstructions prove the non-monophyly of the traditionally recognized subsections Monosegia and Polysegia and their corresponding series, Speciosae and Aphananthae, and Synstyleae and Chorystyleae, respectively. Three morphologically defined species were recovered with high support as monophyletic, namely, Hydrangea panamensis, Hydrangea serratifolia, and Hydrangea tarapotensis. However, statistical support for some shallow nodes did not allow to refute, with high support, the monophyly of several of the herein recognized species for which more than one individual could be analyzed. Based on the obtained phylogenetic framework, we reconstructed the evolution of selected reproductive characters. Hydrangea section Cornidia is the only genus section for which dioecism has been extensively documented. Our character reconstruction of sexual dimorphism shows that dioecism is the ancestral state in this section and that this was reversed to monoecy in Hydrangea seemannii and Hydrangea integrifolia. Character reconstruction for the enlarged marginal flowers recovered their presence as the ancestral character state in H. section Cornidia, although at least three internal lineages independently lost them; thus, losses were reconstructed to be more likely than gain. With respect to the flower color, more species exhibit white than red flowers, and white is reconstructed as the ancestral state. Cornidia also shows an unusual disjunct geographic distribution between Asia and Central Mesoamerica—South America, as it is not present in the USA and Canada. The origin of Cornidia is reconstructed to be the New World with higher probability, and the presence of one species in Asia is likely due to long-distance dispersal.
Highlights
Hortensias are well-known ornamental shrubs, rarely lianas, with an Asian or North American origin (Assocation des Amis de la Collection Nationale d’ Hydrangea Shamrock, 2001; Samain et al, 2010)
One of the least known sections is Hydrangea L. section Cornidia Ruiz and Pav., consisting of lianas that occur from northern Mexico to southern Chile and Argentina with one species, Hydrangea integrifolia Hayata, in southeastern Asia
In clade H (BS = 90), Hydrangea weberbaueri is in a grade with one accession of H. sp. 1 (BS = 72) and a clade (BS = 84) consisting of a sister pair where one clade (BS = 99) is composed of a polytomy of one accession of Hydrangea aff. trianae, one accession of H. trianae, a clade (BS = 90) of two accessions of the latter species, and a clade (BS = 50) where two accessions of H. trianae are in polytomy with Hydrangea goudotii, and another accession of H. aff. trianae
Summary
Hortensias are well-known ornamental shrubs, rarely lianas, with an Asian or North American origin (Assocation des Amis de la Collection Nationale d’ Hydrangea Shamrock, 2001; Samain et al, 2010). One of the least known sections is Hydrangea L. section Cornidia Ruiz and Pav., consisting of lianas that occur from northern Mexico to southern Chile and Argentina with one species, Hydrangea integrifolia Hayata, in southeastern Asia. This section consists of 26 currently accepted species, as well as a yet undefined number of potentially new species and taxa that have been erroneously synonymized (Samain et al, 2014, 2019, 2021; Samain and Martínez Salas, 2015). Hydrangea section Cornidia consists of 26 currently accepted species and a yet undefined number of new species and erroneously synonymized taxa. This clade consists of (sub)tropical lianas occurring from northern Mexico to southern Chile and Argentina, and one species from Southeast Asia.
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