Megahertzia paleoamplexicaulis R.J.Carp. & Rozefelds, 2023

Carpenter, Raymond J. & Rozefelds, Andrew C., 2023, Leaf fossils show a 40 - million-year history for the Australian tropical rainforest genus Megahertzia (Proteaceae), Australian Systematic Botany 36 (4), pp. 312-321 : 314

Megahertzia paleoamplexicaulis R.J.Carp. & Rozefelds , sp. nov.

( Fig. 1, 2.)

Holotype. P257421 ( Fig. 1). Middle Eocene Salt Creek Formation , Eastern View Group ( Holdgate et al. 2001), Anglesea , Victoria. Museum Victoria Christophel collection, Melbourne , Victoria, Australia. A photograph of the holotype is also held in the D. T. Blackburn Palaeobotany Collection, University of Adelaide.

Diagnosis

Fossil leaves conforming closely to M. amplexicaulis in gross morphology and cuticular features.

Description

Leaves ( Fig. 1) mostly incomplete; amplexicaul, typically 3-lobed, entire or sparsely toothed; simple (i.e. unlobed) leaves unknown. Leaf length up to ~ 16 cm; individual lobes ~ 10 cm long and ~ 1.2–2 cm wide (narrow oblong), apex acute and ±falcate, tip spinose. Teeth mostly in apical half of lobes, ~ 0.5–1mm long, apically directed, narrow and ±straight apically and basally (spinose) or convex to slightly concave apically and convex basally, sinus angular. Venation brochidodromous to semicraspedodromous where teeth present; ~10 alternately placed secondary veins per side in lobes, arising at ~45° from midvein, with higher angles near leaf bases. Cuticle of both outer leaf surfaces finely striated with smooth to variably granular inner (periclinal) surfaces; abaxial anticlinal cell wall cuticle more-or-less straight to sinuous and slightly buttressed. Stomatal complexes (i.e. guard cells + subsidiary cells) ( Fig. 2) confined to abaxial side, randomly oriented within distinct small areoles; brachyparacytic, or very rarely, with 1 of the subsidiary cells divided into 2, guard cell length ~24 µm; inner surface cuticle associated with subsidiary cells occasionally with evidence of striations. Trichome bases ( Fig. 2) present but infrequent on both adaxial and abaxial sides, large, associated with multiple underlying epidermal cells (6–30).

Other specimens examined

Museum Victoria registered specimens, glass-mounted in Karo (registered cuticle slide numbers, if corresponding cuticle prepared and stored at MV, in parentheses): P 237339 ( P 243232), P 237493 ( P 243285), P 237500 ( P 243116), P 237527 ( P 231733), P 239637 ( P 242550), P 239643 ( P 243049), P 239644 ( P 242546), P 239645 ( P 242551), P 239653 ( P 242512), P 239654 ( P 242814), P 239656 ( P 242548), P 239666 ( P 242486), P 239689 ( P 242994), P 239691 ( P 242706), P 240210 ( P 243371), P 240221, P 257290 ( P 242808), P 257291 ( Fig. 1) ( P 242809), P 257292 ( P 242810), P 257293, P 257294 ( Fig. 1), P 257295 ( Fig. 2), P 257296, P 257297, P 257298 ( P 243325), P 257299 ( P 243340), P 257300 ( P 243341), P 257301 ( P 243343), P 257302 ( P 243344 and P 231734, Fig. 2), P 257303 ( Fig. 1), P 257858 ( P 243339). The following MV cuticle slides also show Megahertzia ; the location(s) of corresponding leaf specimens are unknown, but photographs of several such leaves with Anglesea specimen numbers (prefix ‘AN’ shown in parentheses) are held at the University of Adelaide: P 231730 ( Fig. 2), P 231732 ( Fig. 2) ( AN 1807, Fig. 1), P 231735 ( Fig. 2), P 242806 ( AN 1806, Fig. 1, 2), P 243120. The location(s) of leaf specimens AN1549, AN1552, AN1769, AN1995 and AN2028 are similarly unknown, but all are accepted in the new species based on photographic evidence. Also stored at MV are a few incomplete leaf impression fossils, including P 236490 and P 236468a, b (part and counterpart).

Etymology

First part of epithet from Greek palaio; named to indicate an ancient occurrence of leaves closely conforming to those of the extant M. amplexicaulis .