ThePentoxylonplant

Abstract

The various dispersed organs belonging to thePentoxylonplant viz.Pentoxylon(stem),Nipaniophyllum(leaf),Sahnia(male flower) andCarnoconites(female cone) have been studied in detail. Apart from the long shoots (type 1 shoots), the plant bore three different kinds of short shoots: the thick woody short shoots, each with a broadly conical head (type 2 shoots); the slender parenchymatous short shoots (type 3 shoots); and the slightly thicker parenchymatous short shoot (type 4 shoot) terminating in aSahniaflower. In addition to the well knownNipaniophyllum raoileaves a second species,N. hobsoniisp. nov., is recognized. InSahniathe sporangiophores were borne on a collar-like structure formed by the raised margin of the receptacle. The broadly conical head of the thick woody short shoot (type 2 shoot) might be the basis of the cone-bearing branchlets ofCarnoconitesfruits. The seeds ofCarnoconitesare spirally arranged rather than being in longitudinal rows as previously suggested.Pentoxylonwas probably a shrubby plant which grew beside water. It sent up erect branched leafy shoots which after a few seasons of growth flopped onto the ground or on other stems, making a thicket. Although the stem,Pentoxylon, resemblesMedullosaandRhexoxylonanatomically, the reproductive parts of the plant,SahniaandCarnoconites, are unlike those of any group of gymnosperms. ThePentoxylonplant is accordingly regarded as an extinct gymnosperm of unknown affinity.Nipanioxylon guptaihas previously been regarded as related toPentoxylon, but its holotype is believed to be a conifer and has nothing to do with thePentoxylonplant.