Figure 5
A reduction and sterilization hypothesis on the evolutionary pathways of female cones of Ephedraceae. (a) A hypothesized archetypal fertile organs of the crown lineage of the Gnetales. (b) Female reproductive units directly terminal to peduncles and bearing no supporting bracts like ephedroid macrofossil Siphonospermum simplex Rydin et Friis [77]. (c) A loosely arranged female cone having multiple pairs of fertile bracts like ephedroid macrofossil Chengia laxispicata gen. et sp. nov. presented herein (Figure 2a–b). (d) A compact female cone bearing multiple whorls of fertile bracts like ephedroid macrofossil Liaoxia robusta Rydin et al. [74]. (e) Reduced tri-ovulate, bi-ovulate, and uni-ovulate female cones bearing only one whorl/pair of fertile bracts like ephedroid macrofossils Ephedra carnosa Yang et Wang [61], E. archaeorhytidosperma Yang et al. [62], E. hongtaoi Wang et Zheng [63], and Gurvanella exquisita Sun et al. and G. dictyoptera Krassilov [67–69]. (f) Reduced and compact female cones of modern Ephedra species bearing only the terminal bract or the uppermost pair/whorl of bracts fertile and the inferior bracts sterile [4, 6, 7, 9].