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Open AccessArticle

Roots Structure and Development of Austrobaileya scandens (Austrobaileyaceae) and Implications for Their Evolution in Angiosperms

Structural and Functional Plant Diversity Group, Institute of Biology, Freie Universität Berlin, Altensteinstrasse 6, 14195 Berlin, Germany
Department of Biological Sciences of State University of New York (SUNY) at Oswego, 30 Centennial Drive, Oswego, NY 13126, USA
Seago Botanical Consulting, Minetto, NY 13115, USA
Author to whom correspondence should be addressed.
Plants 2020, 9(1), 54; (registering DOI)
Received: 21 November 2019 / Revised: 13 December 2019 / Accepted: 23 December 2019 / Published: 1 January 2020
(This article belongs to the Special Issue Root Development)
Since the resolution of the ANA grade [Amborellales, Nymphaeales, Austrobaileyales] as sister to all other flowering plants, a few comparative studies of root structure have suggested that some of their anatomical traits could be of importance to understanding root evolutionary development and angiosperm phylogeny. However, there is still a paucity of information on root structure and apical meristems (RAMs) in these lineages and especially the sister to all other Austrobaileyales, Austrobaileya scandens. We used microtome sections and bright field, epifluorescence, laser confocal, and scanning electron microscopy to study adventitious root RAMs and tissues of A. scandens. Our results indicate that root structure is relatively simple in A. scandens. The epidermis has a thick cuticle and lacks root hairs. The stele is typically diarch, or some modification thereof, and surrounded by a cortex differentiated into a uniseriate endodermis, a middle region sometimes packed with starch, some oil cells, and colonized by arbuscular mycorrhizal fungi, and a multiseriate exodermis. Secondary growth produced many vessel elements in the secondary xylem and scattered sclerenchymatous fibers in secondary phloem. The absence of distinct patterning within the RAM and between the RAM and derivative differentiating tissues shows that the RAM is open and characterized by common initials. Roots structure and anatomy of A. scandens are thus essentially similar to some previously described in Amborella or Illicium in the ANA grade and many magnoliids, and suggest that the first woody flowering plants likely had an open RAM with common initials. Their functional and evolutionary significance in woody early-diverging and basal lineages of flowering plants and gymnosperms remains unclear, but they are clearly ancestral traits. View Full-Text
Keywords: ANA grade; Austrobaileyales; common initials; magnoliids; open meristem ANA grade; Austrobaileyales; common initials; magnoliids; open meristem
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Bachelier, J.B.; Razik, I.; Schauer, M.; Seago, J.L., Jr. Roots Structure and Development of Austrobaileya scandens (Austrobaileyaceae) and Implications for Their Evolution in Angiosperms. Plants 2020, 9, 54.

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