Möller M, Cronk Q C
Royal Botanic Garden, Edinburgh, United Kingdom.
Evolution. 2001 May;55(5):918-29. doi: 10.1554/0014-3820(2001)055[0918:eomnap]2.0.co;2.
Streptocarpus shows great variation in vegetative architecture. In some species a normal shoot apical meristem never forms and the entire vegetative plant body may consist of a single giant cotyledon, which may measure up to 0.75 m (the unifoliate type) or with further leaves arising from this structure (the rosulate type). A molecular phylogeny of 87 taxa (77 Streptocarpus species, seven related species, and three outgroup species) using the internal transcribed spacers and 5.8S region of nuclear ribosomal DNA suggests that Streptocarpus can be divided into two major clades. One of these broadly corresponds to the caulescent group (with conventional shoot architecture) classified as subgenus Streptocarpella, whereas the other is mainly composed of acaulescent species with unusual architecture (subgenus Streptocarpus). Some caulescent species (such as S. papangae) are anomalously placed with the acaulescent clade. Available cytological data are, however, completely congruent with the two major clades: the caulescent clade is x = 15 and the acaulescent clade (including the caulescent S. papangae) is x = 16 (or polyploid multiples of 16). The genera Linnaeopsis, Saintpaulia, and Schizoboea are nested within Streptocarpus. The sequenced region has evolved, on average, 2.44 times faster in the caulescent clade than in the acaulescent clade and this is associated with the more rapid life cycle of the caulescents. Morphological variation in plant architecture within the acaulescent clade is homoplastic and does not appear to have arisen by unique abrupt changes. Instead, rosulate and unifoliate growth forms have evolved several times, reversals have occurred, and intermediate architectures are found. An underlying developmental plasticity seems to be a characteristic of the acaulescent clade and is reflected in a great lability of form.
海角樱草在营养结构上表现出极大的变异。在一些物种中，正常的茎尖分生组织从未形成，整个营养植物体可能由一片巨大的子叶组成，这片子叶长度可达0.75米（单叶类型），或者从这个结构上长出更多叶子（莲座状类型）。利用核糖体DNA的内部转录间隔区和5.8S区域对87个分类单元（77种海角樱草、7种近缘物种和3种外类群物种）进行的分子系统发育分析表明，海角樱草可分为两个主要分支。其中一个大致对应于被归类为海角樱草亚属的具茎类群（具有传统的茎结构），而另一个主要由具有异常结构的无茎物种组成（海角樱草亚属）。一些具茎物种（如帕潘海角樱草）被异常地归入无茎分支。然而，现有的细胞学数据与这两个主要分支完全一致：具茎分支的x = 15，无茎分支（包括具茎的帕潘海角樱草）的x = 16（或16的多倍体倍数）。林奈草属、非洲紫罗兰属和裂瓣苣苔属嵌套在海角樱草属内。测序区域在具茎分支中的进化速度平均比在无茎分支中快2.44倍，这与具茎类群更快的生命周期有关。无茎分支内植物结构的形态变异是同塑性的，似乎并非由独特的突然变化产生。相反，莲座状和单叶生长形式已经进化了多次，出现了逆转，并且发现了中间结构。潜在的发育可塑性似乎是无茎分支的一个特征，并体现在形态的极大易变性上。
