Most Rosaceae flowers are pentamerous and have petals, but subtribe Sanguisorbinae have small tetramerous (or trimerous) flowers without petals, and their floral morphology and morphogenesis remain poorly known. We investigated the floral development of three Sanguisorba spp. using scanning electron microscopy to clarify the relationship between floral development and mature flowers, with emphasis on floral constraints affecting reduction of petals, diversity of androecial patterns and the development of the gynoecium and ovule, and to clarify the pollination mechanisms in the absence of petals. All species have botryoids, with numerous flowers initiated acropetally, and the maturation of flowers follows different directions. All flowers are tetramerous and sepals emerge pairwise. No petal primordia appear. Antesepalous stamens are initiated in a pairwise manner; only S. hakusanensis has a second whorl. The ovary appears inferior by development of a cystiform hypanthium. There is only one ovule with a single integument by reduction of the inner. The space occupied by the larger sepals forces the stamens to develop sequentially. Our data demonstrate that petals are basically absent and that there is a possible shift of pollination mechanisms in Sanguisorba among the mainly wind-pollinated Sanguisorbinae, as both anemophilous and entomophilous characters are found in this genus.

中文翻译：

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Sanguisorba（蔷薇科）的花的形态和形态发生：尽管花瓣减少和空间受限，但花朵仍能多样化

大多数蔷薇科的花是五角星的，并且有花瓣，但是Sanguisorbinae部落有小的四叶（或三叶）花，没有花瓣，其花的形态和形态发生仍然鲜为人知。我们调查了三种Sanguisorba的花期发育spp。使用扫描电子显微镜来阐明花的发育与成熟花之间的关系，重点是影响花瓣减少，雄激素模式的多样性以及妇科和胚珠的发育的花卉约束，并阐明在没有花瓣的情况下的授粉机制。所有物种都有类葡萄球菌，其中有许多花朵是由顶生的，并且花朵的成熟遵循不同的方向。所有花均为四叶形，萼片成对出现。没有花瓣原基出现。前掌雄蕊成对地被发芽。只有白山链球菌有第二个螺纹。由于囊状玻璃托的发育，卵巢表现较差。通过减少内部，只有一个胚珠和单个被膜。较大的萼片占据的空间迫使雄蕊相继发育。我们的数据表明，基本上没有花瓣，并且在主要风传粉的Sanguisorbinae中，Sanguisorba的授粉机制可能发生了转变，因为该属中都发现了嗜性和嗜虫性。