Thaowetsuwan P, Honorio Coronado E N, Ronse De Craene L P
Royal Botanic Garden Edinburgh (RBGE), 20A Inverleith Row, Edinburgh EH3 5LR, UK.
School of Biological Sciences, University of Edinburgh, Daniel Rutherford Building, The King's Buildings, Mayfield Road, Edinburgh EH9 3BF, UK.
Ann Bot. 2017 Nov 10;120(5):819-832. doi: 10.1093/aob/mcx115.
Ophiocaryon is a lesser known genus in Sabiaceae. This study examines flowers of six Ophiocaryon species in comparison with Meliosmaalba, to identify taxonomically informative characters for understanding relationships within the family Sabiaceae, to imply previously unknown pollination mechanisms of Ophiocaryon, and to contribute to the placement of Sabiaceae within the early-diverging eudicots.
Floral morphology and anatomy of six Ophiocaryon species and M. alba were studied and described using scanning electron microscopy, clearing techniques and resin sectioning.
Novel characters of Ophiocaryon were identified, e.g. conical cells on petals, different kinds of orbicules in anthers, stomata on nectary appendage tips and ovary, two distinct surface patterns on stamens and ovary, tanniferous cell layers in the ovary wall, and acorn-shaped unitegmic ovules with very short integuments. Comparison of floral characters between Ophiocaryon and Meliosma found that the calyx, corolla, androecium and gynoecium of Ophiocaryon resemble an undeveloped state of the latter taxon, reflecting a paedomorphic regression of the flower of Ophiocaryon. The flower morphology and anatomy of Ophiocaryon was compared with its putative sister species M. alba, but no clear shared derived characters could be detected. Moreover, the findings of scent, presence of conical cells on petals and a nectary suggest flowers are pollinated by small insects with a secondary pollen presentation on the cupula of fertile stamens.
We found that Ophiocaryon may be derived from ancestors that were similar to extant Meliosma in their flower structure and pollination mechanism. However, the lack of shared derived characters between Ophiocaryon and its phylogenetic sister group M. alba is puzzling and requires further investigations on the diversity of the latter species.
蛇核木属是清风藤科中一个鲜为人知的属。本研究对六种蛇核木属植物的花与毛泡桐进行了比较，以确定有助于理解清风藤科内部关系的分类学信息特征，揭示蛇核木属此前未知的授粉机制，并为清风藤科在早期分化的真双子叶植物中的定位提供依据。
利用扫描电子显微镜、透明技术和树脂切片技术，对六种蛇核木属植物和毛泡桐的花形态和解剖结构进行了研究和描述。
确定了蛇核木属的新特征，例如花瓣上的锥形细胞、花药中的不同类型的珠被绒毡层、蜜腺附属物顶端和子房上的气孔、雄蕊和子房上两种不同的表面模式、子房壁中的含单宁细胞层，以及具极短珠被的橡子形合珠被胚珠。蛇核木属与泡花树属花特征的比较发现，蛇核木属的花萼、花冠、雄蕊群和雌蕊群类似于后者分类群的未发育状态，反映了蛇核木属花的幼态退行。将蛇核木属的花形态和解剖结构与其假定的姊妹种毛泡桐进行了比较，但未检测到明显的共同衍生特征。此外，关于气味、花瓣上锥形细胞的存在以及蜜腺的研究结果表明，花是由小型昆虫授粉的，可育雄蕊的花托上有二次花粉展示。
我们发现蛇核木属可能起源于花结构和授粉机制与现存泡花树属相似的祖先。然而，蛇核木属与其系统发育姊妹群毛泡桐之间缺乏共同衍生特征，这令人费解，需要对后者物种的多样性进行进一步研究。
