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<p>The Neotropical clade of <i>Phlegmariurus</i> is an excellent study system for examining the relationships of the recent morphological and anatomical diversification and changes in habitats of the geologically young Andes, focusing on the process of terrestrialization. Studies of the vegetative axes in species belonging to different natural groups are needed to characterize and infer changes in both epiphytic species of <i>Phlegmariurus</i> and terrestrial species derived from epiphytic ancestors. This work aims to characterize and compare the anatomy of roots, shoots, and inner roots present in the cortex of cauline axes of two epiphytic species, <i>P. mandiocanus</i> and <i>P. sotae</i>, and the terrestrial species <i>P. saururus</i>, as a model to infer the anatomical changes possibly related to the process of terrestrialization in the young Andean habitats in South America. The three species of <i>Phlegmariurus</i> analyzed represent three different lineages: one more early diverging, which includes both epiphytic and terrestrial taxa (<i>P. mandiocanus</i>), one strictly epiphytic (<i>P. sotae</i>), and one strictly terrestrial (<i>P. saururus</i>), showing anatomical characters that could be related to their habit and habitat particularities. The cortex of <i>P. mandiocanus</i>, <i>P. saururus,</i> and <i>P. sotae</i> consists of sclerenchyma and parenchyma. Here, we could corroborate the presence of an endodermis in the three species of Neotropical <i>Phlegmariurus</i> studied. The species analyzed also showed the presence of cortical roots in the cauline axis, which, due to the sclerenchymatous tissue they possess, form support columns in the cortex of this axis. Differences in the distribution of inner cortical roots provide a character trait that distinguishes the species studied. In <i>P. saururus</i> and <i>P. sotae,</i> these roots emerge in the zone of contact with the substrate, whereas in <i>P. mandiocanus,</i> the high number of cortical roots replaces the axis cortex. In the epiphytic <i>P. mandiocanus,</i> the erect habit could be linked to the considerable increase in the number of internal cortical roots. Meanwhile, in the terrestrial <i>P. saururus,</i> the cortical roots have a very thick sclerenchymatous layer on the cortex, which may be associated with the rigid, erect habit of these plants. These differences could be related to the novel reversal to a terrestrial habit.</p>

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Comparative anatomy of roots, shoots and inner cortical roots of Phlegmariurus mandiocanus, P. sotae, and P. saururus (Huperziaceae), related with the process of terrestrialization

  • 期刊论文

  • 发表日期：

    2025年4月16日

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  • María Gabriela Romagnoli,
  • Marcelo D. Arana,
  • Patricia L. Albornoz

摘要

The Neotropical clade of Phlegmariurus is an excellent study system for examining the relationships of the recent morphological and anatomical diversification and changes in habitats of the geologically young Andes, focusing on the process of terrestrialization. Studies of the vegetative axes in species belonging to different natural groups are needed to characterize and infer changes in both epiphytic species of Phlegmariurus and terrestrial species derived from epiphytic ancestors. This work aims to characterize and compare the anatomy of roots, shoots, and inner roots present in the cortex of cauline axes of two epiphytic species, P. mandiocanus and P. sotae, and the terrestrial species P. saururus, as a model to infer the anatomical changes possibly related to the process of terrestrialization in the young Andean habitats in South America. The three species of Phlegmariurus analyzed represent three different lineages: one more early diverging, which includes both epiphytic and terrestrial taxa (P. mandiocanus), one strictly epiphytic (P. sotae), and one strictly terrestrial (P. saururus), showing anatomical characters that could be related to their habit and habitat particularities. The cortex of P. mandiocanus, P. saururus, and P. sotae consists of sclerenchyma and parenchyma. Here, we could corroborate the presence of an endodermis in the three species of Neotropical Phlegmariurus studied. The species analyzed also showed the presence of cortical roots in the cauline axis, which, due to the sclerenchymatous tissue they possess, form support columns in the cortex of this axis. Differences in the distribution of inner cortical roots provide a character trait that distinguishes the species studied. In P. saururus and P. sotae, these roots emerge in the zone of contact with the substrate, whereas in P. mandiocanus, the high number of cortical roots replaces the axis cortex. In the epiphytic P. mandiocanus, the erect habit could be linked to the considerable increase in the number of internal cortical roots. Meanwhile, in the terrestrial P. saururus, the cortical roots have a very thick sclerenchymatous layer on the cortex, which may be associated with the rigid, erect habit of these plants. These differences could be related to the novel reversal to a terrestrial habit.