Atkinson Brian A, Stockey Ruth A, Rothwell Gar W
Department of Botany and Plant Pathology, Oregon State University , Corvallis , OR , United States.
Department of Botany and Plant Pathology, Oregon State University, Corvallis, OR, United States; Department of Environmental and Plant Biology, Ohio University, Athens, OH, United States.
PeerJ. 2016 Dec 21;4:e2808. doi: 10.7717/peerj.2808. eCollection 2016.
Cornaceae consists of 58 species, all within the genus . The Cenozoic record of is extensive and well documented. Molecular divergence-time studies suggest that crown-group may have originated by the Late Cretaceous. However, there has been no formal report of from Cretaceous deposits. Here, we characterize a permineralized fossil fruit assignable to subg. from the Upper Cretaceous (Campanian) Shelter Point locality of Vancouver Island, British Columbia, Canada.
Serial sections of the specimen were made using the cellulose acetate peel technique. Peels were mounted onto microscope slides and studied by light microscopy.
The fossil fruit consists of a tri-locular woody endocarp with dorsal germination valves. The locules are sub-triangular to ellipsoidal in transverse section and are separated by thin septa. Endocarp tissue consists of elongated and isodiametric sclereids and secretory cavities. Internal vascular tissue was not observed, but is interpreted to have been located along the outer periphery of the septa for some length, common in many cornalean taxa. There is one seed in each locule, one of which was found to have endosperm and a dicotyledonous embryo.
Woody endocarps with germination valves, without central vascular bundles, and with one seed per locule are characteristic of several families within the order Cornales. The interpreted vascular pattern and presence of secretory cavities indicates that the fossil fruit is assignable to subg. . Comparative analysis suggests that the fossil is most similar to , a species described from the Paleocene of North Dakota. This fossil is the first evidence of crown-group Cornaceae from the Cretaceous and sheds light on both the plesiomorphic fruit characters and the timing of the initial diversification of the family and basal asterid lineage, Cornales.
山茱萸科由58个物种组成，均属于山茱萸属。山茱萸属的新生代记录广泛且记录详实。分子分歧时间研究表明，山茱萸属冠群可能在晚白垩世就已起源。然而，尚无来自白垩纪沉积物中山茱萸属的正式报道。在此，我们描述了一枚来自加拿大不列颠哥伦比亚省温哥华岛晚白垩世（坎潘阶）谢尔特波因特地点、可归入山茱萸属小花山茱萸亚属的矿化化石果实。
使用醋酸纤维素剥离技术对标本制作连续切片。将切片安装在显微镜载玻片上，通过光学显微镜进行研究。
化石果实由具背生萌发瓣的三室木质内果皮组成。横切面上，子房室呈近三角形至椭圆形，由薄隔膜分隔。内果皮组织由细长和等径的石细胞以及分泌腔组成。未观察到内部维管组织，但据推测在隔膜的外周一定长度范围内存在维管组织，这在许多山茱萸科类群中很常见。每个子房室内有一粒种子，其中一粒种子发现有胚乳和双子叶胚。
具萌发瓣、无中央维管束且每个子房室有一粒种子的木质内果皮是山茱萸目几个科的特征。推测的维管模式和分泌腔的存在表明该化石果实可归入小花山茱萸亚属。比较分析表明，该化石与北达科他州古新世描述的一种物种最为相似。此化石是白垩纪山茱萸属冠群的首个证据，揭示了该科原始果实特征以及该科和基部菊类支系山茱萸目的初始多样化时间。
