State Key Laboratory of Systematic and Evolutionary Botany, Institute of Botany, Chinese Academy of Sciences, 20 Nanxincun, Xiangshan, Beijing, 100093, China.
China Railway Group Limited, 69 Fuxing Road, Beijing, 100039, China.
BMC Evol Biol. 2018 Aug 29;18(1):125. doi: 10.1186/s12862-018-1243-9.
Male cones of modern Ephedraceae are compound and compact. No fossil evidence has so far been found to support an origin of the compact compound male cone from a hypothetical loosely-arranged shoot system.
Here we describe a new macrofossil taxon, Eamesia chinensis Yang, Lin, Ferguson et Wang, gen. et sp. nov., from the Early Cretaceous of western Liaoning, northeastern China. It was an ephedroid shrub bearing male spikes terminal to twigs, but differs from modern Ephedraceae by its loosely-arranged male cones, the axillary male shoot consisting of an elongated synangiophore on which leaf-like foliar organs were inserted, and four sessile synangia terminal to the apex.
The morphology of this fossil suggests that the modern compact male cone of Ephedra was indeed derived from a once loosely-arranged shoot system, and the male reproductive unit originated from a once elongated axillary male shoot. This new fossil species thus provides a transitional link from the hypothetical ancestral shoot system to the modern compact morphology. Changes of habitat from closed humid forests to open dry deserts and shifts of the pollination syndrome may have acted as the driving forces behind this morphological evolution.
现代麻黄科雄性球果为复合紧凑型。到目前为止，还没有化石证据支持从假设的松散排列的枝系系统起源而来的紧凑复合雄性球果。
在这里，我们描述了一个来自中国东北辽宁省西部早白垩世的新的大型化石分类群，杨氏中华麻黄，属和种。它是一种麻黄属灌木，雄性穗状花序着生于小枝顶端，但与现代麻黄科不同的是，其雄性球果排列松散，腋生雄枝由一个拉长的合生体组成，其上插入叶状的叶状器官，四个无梗的合生体位于顶端。
该化石的形态表明，现代麻黄属紧凑的雄性球果确实是从曾经松散排列的枝系系统进化而来的，雄性生殖单位起源于曾经拉长的腋生雄枝。这个新的化石物种为从假设的祖先枝系系统到现代紧凑形态提供了一个过渡环节。生境从封闭潮湿的森林向开阔干燥的沙漠的变化，以及传粉综合征的转变，可能是这种形态进化的驱动力。
