The tribe Spermacoceae (Rubiaceae) in the State of Ceará, northeastern Brazil

Resumen

Tribe Spermacoceae comprises more than 1000 species and about 80 genera, being the largest lineage of herbaceous plants within Rubiaceae. Historically, it is marked by taxonomic complexes. This study aims to investígate the diversity and geographical distribution o f the tribe Spermacoceae in Ceará, in the Northeast región of Brazil. This State covers an area o f 150,000 km2 within the Caatinga domain and is divided into 11 phytoecological units, where the Crystalline Caatinga predominates. Specimens collected from 1990 to 2023, and collections from the EAC, HCDAL, HUEFS, HUVA, and PEUFR herbaria were analysed. The tribe is represented in Ceará by 31 species, of which Borreria savannicola and Mitracarpus fernandesii are endemic to the State, and seven genera, with Borreria being the most diverse (13 spp.), followed by Mitracarpus (six spp.), Hexasepalum (four spp.), Richardia and Spermacoce (three spp. each), andEmmeorhiza and Staelia (one sp. each). In total, 605 collections were verified. Morphological characteristics of fruit, seed, pollen, and intemal indumentum o f the corolla were diagnostic for taxonomic delimitation, with new species having been described for Science in recent years (B. apodiensis, B. savannicola, and H. nordestinum). Borreria scabiosoides has the broadest geographic range, while B. cupularis, B. savannicola, H. nordestinum, and M. polygonifolius are the most restricted species. The northwest región of Ceará is the most diverse (with 22 to 26 species), followed by the south (with 17 to 21 species). The same pattem was verified for the distribution o f records, with the northwest región having the highest numbers (232 to 289 records), whereas the south presents fewer records (59 to 116). Therefore, despite the northwest región having the highest number of species, the greatest diversity relative to the number o f records is found in the Southern región of Ceará.

Acknowledgements: FUNCAP (Process BP5-0197-00136.01.00/22); UVA.