Silva Arthur de Lima, Trovó Marcelo, Coan Alessandra Ike
Departamento de Botânica, Universidade Estadual Paulista "Júlio de Mesquita Filho"-UNESP , Rio Claro , São Paulo , Brazil.
Departamento de Botânica, Universidade Federal do Rio de Janeiro , Rio de Janeiro , Brazil.
PeerJ. 2016 Dec 21;4:e2811. doi: 10.7717/peerj.2811. eCollection 2016.
Flowers in Eriocaulaceae, a monocot family that is highly diversified in Brazil, are generally trimerous, but dimerous flowers occur in and a few other genera. The floral merism in an evolutionary context, however, is unclear. encompasses significant morphological variation leading to a still unresolved infrageneric classification. Ontogenetic comparative studies of infrageneric groups in and in Eriocaulaceae are lacking, albeit necessary to establish evolution of characters such as floral merism and their role as putative synapomorphies.
We studied the floral development and vascularization of eight species of that belong to distinct clades in which dimery occurs, using light and scanning electron microscopies.
Floral ontogeny in dimerous shows lateral sepals emerging simultaneously and late-developing petals. The outer whorl of stamens is absent in all flowers examined here. The inner whorl of stamens becomes functional in staminate flowers and is reduced to staminodes in the pistillate ones. In pistillate flowers, vascular bundles reach the staminodes. Ovary vascularization shows ventral bundles in a commissural position reaching the synascidiate portion of the carpels. Three gynoecial patterns are described for the studied species: (1) gynoecium with a short style, two nectariferous branches and two long stigmatic branches, in most species; (2) gynoecium with a long style, two nectariferous branches and two short stigmatic branches, in ; and (3) gynoecium with long style, absent nectariferous branches and two short stigmatic branches, in .
Floral development of the studied species corroborates the hypothesis that the sepals of dimerous flowers of correspond to the lateral sepals of trimerous flowers. The position and vascularization of floral parts also show that, during dimery evolution in , a flower sector comprising the adaxial median sepal, a lateral petal, a lateral stamen and the adaxial median carpel was lost. In the staminate flower, the outer whorl of staminodes, previously reported by different authors, is correctly described as the apical portion of the petals and the pistillodes are reinterpreted as carpellodes. The occurrence of fused stigmatic branches and protected nectariferous carpellodes substantiates a close relationship between sect. and subg. . Free stigmatic branches and exposed carpellodes substantiate a close relationship between . sect. , . sect. and . ser. . Furthermore, the loss of nectariferous branches may have occurred later than the fusion of stigmatic branches in the clade that groups . subg. and . sect. .
谷精草科是一个在巴西高度多样化的单子叶植物科，其花通常为三轮，但在谷精草属及其他一些属中存在二轮花。然而，从进化角度来看，花部轮数尚不清楚。谷精草属包含显著的形态变异，导致其属下分类仍未解决。尽管有必要通过个体发育比较研究来确定花部轮数等特征的进化及其作为假定共衍征的作用，但目前缺乏对谷精草属及谷精草科属下类群的此类研究。
我们使用光学显微镜和扫描电子显微镜，研究了谷精草属中属于不同分支且出现二轮花的8个物种的花发育和维管束系统。
二轮花谷精草属植物的花发育过程显示，侧萼片同时出现且花瓣发育较晚。在所研究的所有花中，外轮雄蕊均不存在。内轮雄蕊在雄花中发挥功能，在雌花中退化为退化雄蕊。在雌花中，维管束延伸至退化雄蕊。子房维管束系统显示，腹侧维管束在合生位置延伸至心皮的合生成管部分。在所研究的物种中描述了三种雌蕊类型：（1）大多数物种的雌蕊具有短花柱、两个蜜腺分支和两个长柱头分支；（2）谷精草属的某些物种的雌蕊具有长花柱、两个蜜腺分支和两个短柱头分支；（3）谷精草属的另一些物种的雌蕊具有长花柱、无蜜腺分支和两个短柱头分支。
所研究物种的花发育证实了这样的假说，即二轮花谷精草属植物的萼片对应于三轮花的侧萼片。花部各部分的位置和维管束系统还表明，在谷精草属的二轮花进化过程中，一个包含近轴中萼片（adaxial median sepal）、一个侧花瓣、一个侧雄蕊和近轴中心皮的花区缺失了。在雄花中，先前不同作者报道的外轮退化雄蕊被正确地描述为花瓣的顶端部分，而退化雌蕊被重新解释为心皮状结构（carpellodes）。合生柱头分支和具保护作用的蜜腺心皮状结构的出现证实了谷精草属的sect. 与subg. 之间存在密切关系。游离柱头分支和外露心皮状结构证实了谷精草属的sect. 、sect. 与ser. 之间存在密切关系。此外，蜜腺分支的缺失可能比将subg. 和sect. 归为一类的分支中柱头分支的合生出现得更晚。
