Mabea dalyana (Euphorbiaceae-Hippomaneae): a new subshrub with xylopodia endemic to the savannas of the Brazilian Amazon

ABSTRACT During fieldwork in the Campos Amazônicos National Park, Amazonas state, Brazil, a new endemic species of Mabea was collected in savanna areas. Field collections and specimens in RON, MG, and HRCB were analyzed. To understand the species distribution and verify possible areas of occurrence, niche modeling was conducted using the sdm package in R. Mabea dalyana, the new species is a subshrub with xylopodia and reduced size (less than 1 m height) and small, yellow thyrses. There are several allopatric species of Mabea growing in Amazonian savannas, some widespread but others locally restricted, such as M. uleana from central Amazonia that has some superficial resemblance in leaves and inflorescences but can be distinguished from M. dalyana by pubescent adaxial leaf surface (vs. glabrous), 12-21 submarginal glands (vs. 10 submarginal glands), thyrse brownish to red (vs. yellow thyrse) and conspicuous caruncle (vs. caruncle inconspicuous). M. dalyana is endemic to hyperseasonal savanna, very well adapted to savanna, and fire tolerant. It has notable characteristics, such as a subshrub habit, a xylopodium, glabrous leaves, and sepals noticeably larger than the ovary.摘要：在巴西亚马孙州亚马孙坎波斯国家公园开展野外调查期间，研究人员于稀树草原区域采集到马贝属（Mabea）的一个新特有物种。本次研究对RON、MG及HRCB馆藏的野外采集标本与馆藏标本进行了分析。为明确该物种的分布范围并验证潜在适生区域，研究使用R语言中的sdm包开展了生态位建模。本新种为达利马贝（Mabea dalyana），为亚灌木，具木质块根（xylopodium），植株矮小，株高不足1米，具小型黄色聚伞圆锥花序（thyrse）。亚马孙稀树草原中分布有多个马贝属异域物种，部分类群分布广泛，部分则为局域特有；例如产自亚马孙中部的M. uleana，其叶片与花序外观与本种存在一定相似性，但可通过以下特征与达利马贝区分：叶正面被短柔毛（达利马贝叶正面无毛）、具12-21个缘下腺体（达利马贝仅具10个缘下腺体）、聚伞圆锥花序呈棕褐色至红色（达利马贝聚伞圆锥花序为黄色）以及种阜（caruncle）显著（达利马贝种阜不明显）。达利马贝为极端季节型稀树草原特有种，高度适应稀树草原生境且耐火。该物种具有多项突出特征：亚灌木生长习性、木质块根、无毛叶片以及显著大于子房的花萼。