Department of Botany, Natural History Museum, University of Oslo, P.O. Box 1172 Blindern, 0318 Oslo, Norway.
Am J Bot. 2009 Mar;96(3):565-79. doi: 10.3732/ajb.0800208. Epub 2009 Feb 5.
Studies on embryology and seed morphology are complementary to molecular phylogenetics and of special value at the genus level. This paper discusses the delimitation and evolutionary relationships of genera within the tribe Hydrophylleae of the Boraginaceae. The seven Nemophila species characterized by a conspicuous seed appendage are similar in embryology and seed structure. The ovule is tenuinucellate and unitegmic with a meristematic tapetum. The embryo sac penetrating the nucellar apex is of the Polygonum type, has short-lived antipodal cells, and an embryo sac haustorium. The endosperm is cellular, producing two terminal endosperm haustoria, of which the chalazal has a lateral branch. Embryogeny is of the Chenopodiad type (as in Pholistoma). The seed coat is formed from the small-celled inner epidermis of the integument. The large-celled outer epidermis of the integument disintegrates into scattered cells. Seed pits evolve from irregularly placed inner epidermal cells of the integument. The chalazal part of the ovule produces a cucullus, that functions as an ant-attracting elaiosome. Those species of Nemophila with a conspicuous cucullus form a natural genus. Nemophila is most closely related to Pholistoma. The integumentary seed pits of Nemophila might have evolved from ovular seed pits similar to those in Pholistoma.
胚胎学和种子形态学的研究与分子系统发育学相辅相成，在属的水平上具有特殊的价值。本文讨论了紫草科琉璃草族属的界定和进化关系。具有明显种脐附属物的七个Nemophila 种在胚胎学和种子结构上具有相似性。胚珠薄珠心，具单珠被，具分生组织的绒毡层。穿透珠心顶端的胚囊为Polygonum 型，具短命的反足细胞和胚囊吸器。胚乳为细胞型，产生两个顶端胚乳吸器，其中合点端具有侧枝。胚的发生属于藜科型（如 Pholistoma）。种皮由珠被的小细胞内层表皮形成。珠被的大细胞外层解体为散在的细胞。种脐从珠被的内表皮不规则排列的细胞进化而来。胚珠的合点部分产生一个帽状体，起到吸引蚂蚁的作用。具有明显帽状体的Nemophila 种形成一个自然属。Nemophila 与 Pholistoma 关系最为密切。Nemophila 的珠被种脐可能是从类似于 Pholistoma 的胚珠种脐进化而来的。
