New records of colleters in Chamaecrista (Leguminosae, Caesalpinioideae s.l.): structural diversity, secretion, functional role, and taxonomic importance

Abstract

Premise of research. Colleters are structures that secrete a sticky product that covers and protects the shoot apex and floral buds. In Chamaecrista, colleters have been reported in the cotyledons of three species and on the leaves of all species belonging to sect. Absus subsect. Baseophyllum. Anatomical studies using taxonomic and phylogenetic approaches are necessary to evaluate the presence, diversity, and importance of colleters for Chamaecrista. Methodology. We analyzed 55 species of Chamaecrista belonging to five of the six sections of the genus. Samples from both herbarium- and field-collected material of young vegetative and reproductive meristems were used. The material was subjected to standard anatomical study by light microscopy and SEM, and secretion was evaluated by histochemical analyses. Pivotal results. Histochemical analyses for the total proteins, total polysaccharides, acid mucopolysaccharides, pectins/mucilage, and lipids generated positive results. Six types of colleters are described here: club shaped, racket shaped, long bottle shaped, short bottle shaped, long digitiform, and short digitiform. Sect. Apoucouita showed the short digitiform and club-shaped types and was the only section with colleters on the sepal margins. Most species of sect. Absus subsect. Absus presented the short bottle-shaped type, while all species from subsect. Baseophyllum presented the short digitiform and club-shaped types. Although the short bottle-shaped type was the most common among species from sect. Chamaecrista, the short digitiform and club-shaped types were also observed. The short bottle-shaped colleters were also found in sect. Grimaldia, while in sect. Xerocalyx only the digitiform type was found. Conclusions. The topography and components identified in the secretion of the colleters suggests that such structures may be involved in the protection of developing leaves and flowers. Five of the six types described in our study are novelties for Chamaecrista. The distribution of colleter structural diversity provides an important source of new data that may help to clarify the taxonomy and phylogeny of Chamaecrista.