A NEW IRIDOPTERIDALEAN PLANT FROM THE MIDDLE DEVONIAN OF NORTHWEST CHINA

Middle Devonian (Givetian) plant Ramophyton givetianum gen. et sp. nov. is reported from north Xinjiang of northwest China. All axes of this plant are smooth. First-order axes are pseudomonopodial in habit and bear alternately attached second-order axes in the same plane. Numerous ultimate appendages are arranged in whorls on both first- and second-order axes, are equally dichotomized in three dimensions, and form paired tips curving oppositely. Two to five ultimate appendages per whorl are unequally spaced at the nodes of first- order axes, and two to four appendages per whorl are similarly spaced at nodes of second-order axes. A single second-order axis and two or three ultimate appendages are inserted in one node of first- order axes. The ultimate appendages are sterile or fertile or contain both sterile and fertile parts. The curved tips of fertile ultimate appendages bear tiny elliptical sporangia in pairs. Ramophyton is attributed to Iridopteridales mainly because of elongate terminal sporangia in pairs, iterative architecture of whorled branching, and two types of lateral organs (ultimate appendages and second-order axes) on one node of first- order axes. I suggest that iridopteridalean and pseudosporochnalean cladoxylopsids show close affinity because they share elongate terminal sporangia in pairs and similar fertile/sterile ultimate appendages; nonpseudosporochnalean cladoxylopsids display major differences in fertile complexity/diversity and distinct planation.