L. H. Bailey Hortorium, Department of Plant Biology, 228 Plant Science Building, Cornell University, Ithaca, New York 14853 USA.
Am J Bot. 2003 Sep;90(9):1373-88. doi: 10.3732/ajb.90.9.1373.
Fossilized flowers and fruits from the Upper Cretaceous (Turonian, ca. 90 million years [my] before present) Raritan Formation of New Jersey are described as the new genus Divisestylus with two species, D. brevistamineus and D. longistamineus. The fossils are fusainized and three-dimensionally preserved. Morphological characteristics suggest affinities with extant Saxifragaceae and Iteaceae, two closely related families in Saxifragales. Similarities include a pentamerous perianth, calyx fused below into a hypanthium with free sepal lobes above, haplostemonous androecium with stamens situated opposite the calyx lobes, inferior ovary, bicarpellate gynoecium, numerous ovules on axile placentas, conspicuous intrastaminal nectary ring, and capsulate fruit opening apically. The unique fusion of the gynoecium, with carpels and stigmas fused but styles free, indicates closer affinities with extant Iteaceae, whereas other characters, such as basifixed anthers in D. brevistamineus, tricolpate and striate pollen grains, and anomocytic stomata, indicate closer affinities to Saxifragaceae. Cladistic analyses utilizing molecular data from a previously published analysis and morphological data as well as morphological data alone demonstrate the fossils share a more recent common ancestor with Iteaceae than Saxifragaceae, thereby making Divisestylus the oldest fossils known with clear affinities to Iteaceae.
描述了来自新泽西州上白垩统（Turonian，约 9000 万年前）Raritan 组的已灭绝的花和果实，它们被归为新属 Divisestylus，有两个种，D. brevistamineus 和 D. longistamineus。这些化石是煤化的，三维保存。形态特征表明与现生虎耳草科和卫矛科有关，这两个科在虎耳草目中关系密切。相似之处包括五瓣花被、花萼在下部合生为托杯，上部有自由的萼裂片，单室雄蕊，雄蕊与萼裂片相对，下位子房，二心皮雌蕊，轴生胎座上有许多胚珠，明显的雄蕊间蜜腺环，蒴果顶端开裂。雌蕊独特的融合，心皮和柱头合生但花柱自由，表明与现生卫矛科的亲缘关系更近，而其他特征，如 D. brevistamineus 的基着花药、三沟和条纹花粉粒以及不等细胞型气孔，表明与虎耳草科的亲缘关系更近。利用先前发表的分析中的分子数据和形态数据以及仅形态数据进行的系统发育分析表明，化石与卫矛科的共同祖先比与虎耳草科更近，因此 Divisestylus 是已知与卫矛科关系最密切的最早化石。
