Revisão e atualização dos parâmetros para classificação dos tricomas em Croton l. (Euphorbiaceae).

Abstract

Trichomes are epidermal appendages that have a variety of forms and can be classified in different ways, they are attributes used in botany for auxiliary taxonomic studies and have been proven for several families. These structures have helped in infrageneric delimitations in Croton, making trichome typologies an important taxonomic character. There is an article widely used for the classification of trichomes in Croton, but given the inconsistencies produced, different methods of analysis used alone and the lack of clear and standardized parameters for defining the typologies. It was necessary to review the most used classification for Croton considering new anatomical and morphological information, and to propose a new classification of trichomes for the genus based on an extensive inventory, establishing parameters that encompass all its morphological and phylogenetic diversity. From a database, fed by experts in Euphorbiaceae and analysis of clearing images and scanning electron microscopy, we analyzed 94 species, complemented with literature review of 102 species, with all material distributed in 18 sections of Croton. A single type of capitate glandular trichome and six types of tector trichomes were recognized: simple, starry, pin cushion, dendritic, multiradiated and lepidote, in addition to their subtypes. Simple trichome was recognized as a type of trichome and not a reduction transition from stellate and multiradiate type, it consisted of synonyms of fasciculated to stellate types, and rosulate to multiradiate types, reflecting the update of the previously considered fasciculated cuhion shaped in pin cushion, in the observation of the porrecto arm in dendritic trichomes and in the reduction of the 5 subtypes of lepidote into only partially or fully fused lepidote. This study consisted of establishing parameters and terminology in a robust sampling, demonstrating fundamental aspects for a universal classification.