Redefinition of Stachytarpheta sprucei (Verbenaceae) reveals a remarkable geographic disjunction in tropical forests of South America

ABSTRACT Stachytarpheta is the second largest genus of Verbenaceae, mainly distributed in xeric habitats of South America. The morphological revision of South American specimens clarified the taxonomic identity of three previously accepted species from informal group Gesnerioides: S. sprucei (from the Amazon Forest domain), S. alata, and S. tomentosa (from the Atlantic Forest domain). A new taxonomic arrangement is proposed here, with the synonymization of S. alata and S. tomentosa under S. sprucei. Consequently, the newly circumscribed S. sprucei evidences a remarkable geographic disjunction, with populations separated by the Caatinga, Cerrado, and Chaco domains (the South American dry diagonal). It inhabits inselbergs, tepuis, and savannas in the Amazon Forest domain, and top of inselbergs surrounded by forest in the Atlantic Forest domain. A detailed species description, taxonomic comments, a geographic distribution map, photos of living specimens, and an identification key to the species from the Gesnerioides group are included.

摘要：假马鞭属（Stachytarpheta）为马鞭草科（Verbenaceae）第二大属，主要分布于南美洲旱生生境。本研究对南美标本开展形态学修订，明确了此前归入盖氏非正式类群（Gesnerioides）的3个物种的分类学归属：分别为分布于亚马逊森林域的斯普鲁斯假马鞭（S. sprucei）、翅茎假马鞭（S. alata）以及分布于大西洋森林域的绵毛假马鞭（S. tomentosa）。本研究提出全新分类处理方案，将翅茎假马鞭与绵毛假马鞭作为异名归并入斯普鲁斯假马鞭。经此修订后，新界定的斯普鲁斯假马鞭呈现出显著的地理间断分布格局，其种群被卡廷加（Caatinga）、塞拉多（Cerrado）与查科（Chaco）植被区（即南美干旱对角线）相互分隔。该物种的栖息生境包括亚马逊森林域的岩质岛山（inselbergs）、特普伊高原（tepuis）与稀树草原，以及大西洋森林域中被森林环绕的岩质岛山顶部。本研究包含该物种的详细形态描述、分类学评述、地理分布图、活体标本照片，以及盖氏类群物种的鉴定检索表。