Instituto de Botánica Darwinion, Labardén 200, San Isidro, Buenos Aires, Argentina.
Ann Bot. 2010 Jul;106(1):107-30. doi: 10.1093/aob/mcq090.
Twenty-five genera having sterile inflorescence branches were recognized as the bristle clade within the x = 9 Paniceae (Panicoideae). Within the bristle clade, taxonomic circumscription of Cenchrus (20-25 species), Pennisetum (80-140) and the monotypic Odontelytrum is still unclear. Several criteria have been applied to characterize Cenchrus and Pennisetum, but none of these has proved satisfactory as the diagnostic characters, such as fusion of bristles in the inflorescences, show continuous variation.
A phylogenetic analysis based on morphological, plastid (trnL-F, ndhF) and nuclear (knotted) data is presented for a representative species sampling of the genera. All analyses were conducted under parsimony, using heuristic searches with TBR branch swapping. Branch support was assessed with parsimony jackknifing.
Based on plastid and morphological data, Pennisetum, Cenchrus and Odontelytrum were supported as a monophyletic group: the PCO clade. Only one section of Pennisetum (Brevivalvula) was supported as monophyletic. The position of P. lanatum differed among data partitions, although the combined plastid and morphology and nuclear analyses showed this species to be a member of the PCO clade. The basic chromosome number x = 9 was found to be plesiomorphic, and x = 5, 7, 8, 10 and 17 were derived states. The nuclear phylogenetic analysis revealed a reticulate pattern of relationships among Pennisetum and Cenchrus, suggesting that there are at least three different genomes. Because apomixis can be transferred among species through hybridization, its history most likely reflects crossing relationships, rather than multiple independent appearances.
Due to the consistency between the present results and different phylogenetic hypotheses (including morphological, developmental and multilocus approaches), and the high support found for the PCO clade, also including the type species of the three genera, we propose unification of Pennisetum, Cenchrus and Odontelytrum. Species of Pennisetum and Odontelytrum are here transferred into Cenchrus, which has priority. Sixty-six new combinations are made here.
在 x = 9 的 Paniceae（Panicoideae）中，有 25 个属被认为具有不育的花序枝，它们被归类为刚毛群。在刚毛群中，Cenchrus（20-25 种）、Pennisetum（80-140）和单种的 Odontelytrum 的分类界限仍然不清楚。已经应用了几个标准来描述 Cenchrus 和 Pennisetum，但这些标准都没有被证明是令人满意的诊断特征，例如花序中刚毛的融合表现出连续的变化。
本研究基于形态学、质体（trnL-F、ndhF）和核（knotted）数据，对代表属的物种进行了系统发育分析。所有分析均采用启发式搜索，采用 TBR 分支交换进行简约性分析。分支支持通过简约性 jackknifing 进行评估。
基于质体和形态学数据，Pennisetum、Cenchrus 和 Odontelytrum 被支持为一个单系群：PCO 群。只有 Pennisetum 的一个节（Brevivalvula）被支持为单系群。P. lanatum 在不同的数据分区中的位置不同，尽管质体和形态学以及核分析的组合表明该物种是 PCO 群的成员。基本染色体数 x = 9 被认为是原始的，而 x = 5、7、8、10 和 17 是衍生状态。核系统发育分析揭示了 Pennisetum 和 Cenchrus 之间的网状关系模式，表明至少有三个不同的基因组。由于无融合生殖可以通过杂交在物种之间转移，因此它的历史很可能反映了杂交关系，而不是多个独立的出现。
由于目前的结果与不同的系统发育假设（包括形态学、发育和多基因座方法）之间的一致性，以及对 PCO 群的高度支持，包括三个属的模式种，我们建议将 Pennisetum、Cenchrus 和 Odontelytrum 统一起来。Pennisetum 和 Odontelytrum 的物种现被转移到 Cenchrus 中，后者具有优先权。这里提出了 66 个新组合。
