作 者:Yang Y, Wang Q*
影响因子: 3.73
刊物名称: PLoS One
出版年份: 2013
卷: 8 期: 1 页码: e53652
文章摘要
Bracts
of female cones of extant gymnosperm Ephedra (Joint fir) are either
colorful and fleshy (section Ephedra), or dry-winged and membranous
(section Alatae), or dry and coriaceous (section Asarca), which have
played a crucial role in long-distance seed dispersal that is
responsible for a wide distribution of the genus in semiarid and arid
areas of Eurasia, North Africa, North America, and South America. Recent
molecular systematic studies on Ephedra have suggested that the fleshy
bracts in character evolution may be plesiomorphic relative to the dry,
membranous and coriaceous bracts. However, little is known about when
the fleshy bracts of Ephedra have made their debut in the geological
past. Herein, we describe a novel, fleshy bract-bearing female cone
macrofossil from the Early Cretaceous (ca. 120-125 Ma) Yixian Formation
in Liaoning, northeastern China. This cone bears three ellipsoid seeds
subtended by only one whorl of fleshy bracts. Each seed has a thin outer
envelope and an inner integument that extends upward and passes through
the opening of the outer envelope, forming a thin and straight
micropylar tube. Such a syndrome shows the closest similarity to an
extant triovulate species Ephedra intermedia in the section Ephedra, but
the latter bears a whorl of terminal fertile bracts and more than one
whorl of inferior sterile bracts, and a thick outer envelope. Hence, we
establish a new fossil species Ephedra carnosa. Our discovery provides
the first direct macrofossil evidence for the previous molecular
systematics of Ephedra, implying that the origin of fleshy bracts in
Ephedra should not have been later than that of the membranous and
coriaceous bracts by at least the Early Cretaceous.
原文下载 : 74.121222.pdf