The Southern Hemisphere family Casuarinaceae has a long fossil record, both macrofossils and pollen, none of which provides any evidence about the morphology of the precursor to the family. However, it has long been considered, from both molecular phylogenies and morphological data, that the extant genus Gymnostoma retains key ancestral states and the highly reduced leaf area is a result of a scleromorphic response to low soil nutrients. Gymnostoma has by far the earliest, most extensive and best preserved macrofossil record, beginning in the Late Paleocene. Modification of the stomatal location from superficial in Gymnostoma to encrypted in furrows in the other genera assisted in water conservation as species evolved. We conclude that the morphology of the living and fossil vegetative branchlets provides evidence that low soil nutrients (especially phosphorus) and high water availability in a relatively light limited environment were the original drivers for evolution in the Casuarinaceae. Reducing water availability (xeromorphy) in progressively higher light environments were the major drivers of post-Eocene evolution in this unique plant family.

中文翻译：

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木麻黄科在澳大利亚新生代低土壤养分和干旱气候下进化的化石证据

南半球木麻黄科有很长的化石记录，包括大型化石和花粉，没有一个提供关于该科前体形态的任何证据。然而，长期以来人们一直认为，从分子系统发育和形态学数据来看，现存的裸口鱼属保留了关键的祖先状态，叶面积的大幅减少是对低土壤养分的硬化反应的结果。Gymnostoma 是迄今为止最早、最广泛和保存最完好的大型化石记录，始于晚古新世。随着物种进化，将气孔位置从裸口纲的浅表修改为其他属的犁沟中的加密有助于水源保护。我们得出结论，活的和化石的营养小枝的形态提供了证据，证明在相对光线有限的环境中，土壤养分含量低（尤其是磷）和水分利用率高是木麻黄科进化的原始驱动因素。在逐渐增强的光照环境中减少水的可用性（异形）是这个独特植物家族中始新世后进化的主要驱动力。