Early evidence of xeromorphy in angiosperms: Stomatal encryption in a new eocene species ofBanksia(Proteaceae) from Western Australia

Abstract

The presence of B. paleocrypta within the center of diversity of subgenus Banksia in edaphically ancient southwestern Australia is consistent with the continuous presence of this lineage in the region for ≥40 Ma, a testament to the success of increasingly xeromorphic traits in Banksia over an interval in which numerous other lineages became extinct.

Fossil evidence for open, Proteaceae‐dominated heathlands and fire in the Late Cretaceous of Australia

“…Although gymnosperms are now present in southwestern Australia ( Podocarpus , callitroid Cupressaceae and Macrozamia ), these gymnosperms belong to clades that, on the basis of molecular evidence, are probably much younger than Cretaceous age (Piggin and Bruhl, 2010; Biffin et al, 2011; Ingham et al, 2013). However, HUC11 gymnosperm taxa including Araucariaceae, Dacrydium , Dacrycarpus , Phyllocladus and a range of ferns are known from Eocene macrofossils in southwestern Australia (Hill and Merrifield, 1993; McLoughlin and Hill, 1996; Carpenter et al, 2014), and palynostratigraphic evidence suggests that these taxa persisted there until the mid‐Pliocene, when they occurred as rare elements within local, fire‐affected sclerophyll vegetation not unlike that in the SWAFR today (Bint, 1981; Atahan et al, 2004; Dodson and Macphail, 2004). Banksia leaves were also prominent in the Eocene of southwestern Australia and are suggestive of a very long, continuous history in the region (Carpenter et al, 2014).…”

Testing the Biases in the Rich Cenozoic Angiosperm Macrofossil Record

“…As a result, there were few lakes formed by lava flows, landslips, faulting, and volcanic eruptions. Moreover, it is possible that relatively large areas of central and northern Australia were too dry for fossilization during much of the Cenozoic (Carpenter et al 2014). The poor fossil record of Antarctica is due mainly to the presence of a permanent ice sheet since the Miocene (Zachos et al 2001).…”

Eocene palynology of the Mulga Rocks deposits, southern Gunbarrel Basin, Western Australia

“…However, such species are only present in very low percentages at Mulga Rocks. Carpenter et al (2014) noted that pollen affiliated with Dacrycarpus and Dacrydium was present in sediments as young as Pliocene age in southwestern Australia, persisting as climates changed to seasonally dry and even after aridity was noted to be prevalent across much of Australia in the Miocene.…”

“…Proteaceous leaves are well represented within the late Eocene Kojonup Sandstone flora, with particularly abundant Banksia-like leaves (McLoughlin & Hill 1996, McLoughlin & McNamara 2001. A new Banksia species with evidence of xeromorphic features has recently been described from this flora (Carpenter et al 2014) implying habitats drier than typical rainforests. Carpenter & Pole (1995) also recognized a high diversity of Proteaceae together with several Banksieae and a few Myrtaceae specimens among 42 cuticle samples studied from late Eocene sediments in the Cowan and Lefroy palaeodrainages.…”

“…having thick leaves and a lack of rainforest adaptations, such as drip tips. This has been recognized for several Cenozoic leaf floras studied in southern WA (Hill & Merrifield 1993, McLoughlin & Hill 1996, Carpenter & Pole 1995 and by the recent description of a Banksia species with xeromorphic characters (Carpenter et al 2014). Of particular interest is the Myrtaceae-dominated West Dale macroflora from the Wheatbelt of WA (Hill & Merrifield 1993).…”