Data from: Phylogeny and circumscription of Cephalocereus (Cactaceae) based on molecular and morphological evidence

Cephalocereus, Neobuxbaumia, and Pseudomitrocereus (Cactaceae, Cactoideae, Echinocereeae) are related genera of columnar cacti native to Mexico with current ambiguous circumscription. We applied maximum parsimony and Bayesian inference methods to reconstruct the phylogeny of the Cephalocereus group using molecular data from seven chloroplast regions (petL-psbE, psbA-trnH, rpl16, rpl32-trnLUAG, trnL-F, trnQrps16, andycf1), simple coded indels, and 46 structural characters. The Cephalocereus group was recovered as monophyletic with high support values, whereas Neobuxbaumia appeared as paraphyletic, due to the polyphyly of Cephalocereus and the derived position of Pseudomitrocereus within this group. Topology was mostly congruent among the different phylogenetic methods explored, and three pervasive clades were observed. Two structural characters were confirmed as synapomorphies for the Cephalocereus group: prismatic crystals in the dermal system and a perianth woody cap persistent in the fruit. The derived position of Pseudomitrocereus suggests that new hypotheses must be explored regarding the possible hybrid origin of this taxon. We propose the transfer of all species of Neobuxbaumia, Cephalocereus, and Pseudomitrocereus to a single genus, in which Cephalocereus takes priority over the other names. Based on our results, a new circumscription for Cephalocereus is proposed, including a taxonomic synthesis, two new combinations (Cephalocereus multiareolatus and Cephalocereus sanchezmejoradae), and a key for species.头花仙人掌属（Cephalocereus）、新布克巴米亚属（Neobuxbaumia）与假小槌柱属（Pseudomitrocereus）隶属于仙人掌科（Cactaceae）仙人柱亚科（Cactoideae）鹿角柱族（Echinocereeae），为原产于墨西哥的柱状仙人掌近缘属，其分类界定目前尚存歧义。本研究采用最大简约法与贝叶斯推断法，基于7个叶绿体区域（petL-psbE、psbA-trnH、rpl16、rpl32-trnL<UAG>、trnL-F、trnQ-rps16及ycf1）的分子数据、简单编码的插入缺失（indels）以及46个形态结构性状，对头花仙人掌类群开展系统发育重建。分析结果显示，头花仙人掌类群为高支持度的单系群，而新布克巴米亚属呈现并系特征，这源于头花仙人掌属本身为多系群，且假小槌柱属在该类群中处于衍生演化位置。不同系统发育分析方法所得到的拓扑结构整体一致性较高，共识别出3个稳定演化支。本研究确认有2个结构性状可作为头花仙人掌类群的共源性状：表皮系统中的棱柱形晶体，以及宿存于果实中的花被木质化帽状体。假小槌柱属的衍生演化位置提示，需针对该类群的潜在杂交起源展开新的研究假说。本研究提议将新布克巴米亚属、头花仙人掌属与假小槌柱属的所有物种合并至单一属中，其中头花仙人掌属的命名优先权优先于其余两属。基于本研究结果，我们提出头花仙人掌属的新分类界定，包含分类学综论、2个新组合种（Cephalocereus multiareolatus、Cephalocereus sanchezmejoradae）以及物种检索表。