Fig. 5.

Basal to distal sections of petiole bases of Osmunda pulchella sp. nov. from the Lower Jurassic of Skåne, southern Sweden (NRM-S069657), showing successive stages of petiole-base differentiation. a Parenchymatous inner cortex and petiolar wings. b–e Development of an abaxial arch of thick-walled fibres in the sclerenchyma ring. c Appearance of a sclerenchyma patch in the bundle concavity. d Appearance of a sclerenchyma mass in the petiolar wing. f Sclerenchyma ring with two prominent lateral masses of particularly thick-walled fibres. g Collapsed outermost petiole (note rock matrix above) showing sclerenchyma ring with one abaxial and two lateral masses of particularly thick-walled fibres, and elongate sclerenchyma strips (e.g. bottom, right) isolated from degraded stipular wings of adjacent petioles. Scale bars = 500 μm