Phylogenetic position and evolution of glandular structures of the unusual and narrowly distributed genus Rhytidanthera (Ochnaceae)

Abstract

Rhytidanthera is the only genus of Ochnaceae with compound leaves, and it forms sparse, small populations restricted to the primary forest of the Colombian and Venezuelan Andes and the sandstone hills of La Macarena and Chiribiquete. It has been suggested to be related to Godoya, Cespedesia and Krukoviella in taxonomic and phylogenetic studies. However, the relationships in this group remain poorly resolved, due to the lack of a wider molecular and taxonomic sampling. We present a phylogenetic study of tribe Sauvagesieae including three Rhytidanthera spp. and one species each of Godoya and Cespedesia, using sequences from one nuclear (ITS) and four plastid DNA regions (matK, ndhF, rbcL and trnL-F), in order to clarify the relationships among these four genera. We recover a new and well-supported phylogenetic hypothesis, with Rhytidanthera as sister to a clade comprising Godoya and the clade formed by Cespedesia and Krukoviella. This Neotropical clade was recovered as sister to the monotypic and African genus Fleurydora. The clade comprising Rhytidanthera, Godoya, Cespedesia and Krukoviella is supported by the presence of glandular structures (colleters) at the base of stipules and bracts. The colleters also evolved at the base of the sepals in this clade, with a secondary loss in Cespedesia and Krukoviella. We suggest that the combination of unequal-sized sepals enclosing the floral bud and the presence of colleters in members of this clade could have a role in the protection of leaves and flowers in the early stages of development, instead of acting in pollinator attraction.

Phylogenomics of the tropical plant family Ochnaceae using targeted enrichment of nuclear genes and 250+ taxa

“…The African Fleurydora is sister to the remainder, which are all neotropical, with Rhytidanthera retrieved as sister to a poorly resolved clade of Godoya , Krukoviella and Cespedesia . This confirms the findings of a recent study based on five DNA regions (Reinales & Parra‐O., 2020). There is also support from morphology for this clade: Godoya , Krukoviella , Cespedesia and Rhytidanthera are all united, among others, by the same carpel and ovule numbers, the coriaceous capsules with alate seeds and a peculiar leaf venation with scalariform net‐like third‐order veins (Amaral, 1991; Schneider & al., 2014; Schneider & al., 2017).…”

“…It is the only genus with pinnately compound leaves in the subfamily. All four genera also share the presence of colleters (i.e., glandular hairs) on stipules, bracts and sepals (lost on sepals in Cespedesia and Krukoviella ; Reinales & Parra‐O., 2020). Flower zygomorphy only at anthesis (in contrast to its presence already in bud as in Luxemburgieae) unites this clade with Blastemanthus and Fleurydora , but this character was identified as plesiomorphic (Schneider & al., 2014).…”

Colleters, Extrafloral Nectaries, and Resin Glands Protect Buds and Young Leaves of Ouratea castaneifolia (DC.) Engl. (Ochnaceae)

“…Standard colleters occur in several taxa of angiosperms, most notably the Rubiaceae and Apocynaceae [ 9 , 21 , 22 , 26 ]. Colleters or colleter-like glands (i.e., thick glandular hairs) have been reported in a few species of Ochnaceae, although usually associated with the inner base of stipules, sepals, or leaves [ 14 , 15 , 16 ]. Marginal glands, however, are commonly reported in Sauvagesia [ 15 , 27 , 28 ] and several additional genera of the subfamily Sauvagesioideae [ 14 ].…”

“…Although there are controversies about the definition of colleters, the functional aspect seems to be preponderant for recognizing these structures [46,47]. While the scales and stipules of O. castaneifolia have resin glands formed essentially by a secretory epithelium, Reinales and Parra-O [16] described the presence of standard colleters in scales and stipules for the clade comprising Rhytidanthera, Godoya, Cespedesia, and Krukoviella. It is important to note that these colleters and resin glands have similar secretory activity and, most likely, perform the same function.…”

“…Knowledge regarding chemical defenses in shoot buds of Ochnaceae is far from comprehensive, although nectar secretion in scales and stipules of some taxa is well known. Many authors have recently reported the presence of glands in the family [ 14 , 15 , 16 , 17 ], sometimes relating them to bud protection [ 16 ]. Nevertheless, many aspects of secretion in the family are still poorly understood.…”