Hicklingia is a genus of extinct plants of the Middle Devonian (around ). Compressed specimens were first described in 1923 from the Old Red Sandstone of Scotland.[, cited in ] Initially the genus was placed in the "", but this group is defined as having terminal Sporangium (spore-forming organs), and later work showed that the sporangia of Hicklingia were lateral rather than strictly terminal, so that it is now regarded as having affinities with the .
Description
The
sporophyte had a tufted growth habit, with narrow leafless stems (axes) up to 17 cm high which branched dichotomously. Sporangia were borne on short stalks (up to 3 mm), on all sides of the stem and also terminally. There are oval scars on specimens where the stalks are presumed to have broken off. The lateral sporangia were closely adpressed to the stem. The effect is of a 'spike' of sporangia which terminates some stems. The sporangia opened via slits, but these did not have the thickened borders which are a feature of some
Zosterophyllum species. The
vascular tissue of the stem was not observed.
are up to 50 μm in diameter and trilete.
[, p. 254] The
gametophyte is not known.
Phylogeny
The affinity with zosterophylls is recognized in the
cladogram published in 2004 by Crane et al. in which
Hicklingia is placed as a sister to all the other
Lycopodiophyta (living and extinct clubmosses and relatives).
Hao and Xue in 2013 listed the genus as a zosterophyll.[
]
External links
