Fig. 3

An overview of wood diversity in Tordylieae (A-E) and outgroup (F) in transverse sections. A H. sphondylium: cambial activity is confined to fascicular zone (within vascular bundles), where cambium-derived fibres are present, interfascicular zones are occupied by medullary rays. B Nanobubon hypogeum: a section identified as a root due to the missing parenchymatous pith. Cambial activity is best evidenced by wide secondary phloem; the background tissue consists exclusively of parenchyma. C Capnophyllum lutzeyeri: a continuous, very narrow cylinder of secondary xylem that consists of fibrous background tissue and few vessel elements. D Notobubon pearsonii: a wide cylinder of fibrous secondary xylem with five growth ring boundaries marked by change in vessel size and production of thick-walled fibres in latewood. E Ducrosia flabellifolia: the outer part of secondary xylem with exclusively parenchymatous background tissue. F Pycnocycla nodiflora: fibrous secondary xylem with growth ring boundaries marked by marginal parenchyma and vague dendritic disposition of vessels