A Comparative Study of Stigmarian Appendages and Isoetes Roots

Stewart, Wilson N.

doi:10.1002/j.1537-2197.1947.tb12995.x

Cited by 30 publications

(1 citation statement)

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“…For instance, morphological identity and homology of the rooting system of extant Isoetes with that of Paleozoic rhizomorphic lycophytes (e.g. Paralycopodites and Sigillaria ; Stewart, ; Karrfalt, ; Jennings et al ., ; Rothwell & Erwin, ; Hetherington et al ., ; Hetherington & Dolan, ) demonstrates conservation of developmental characters and body plan organization over > 300 Myr. Or, to consider an even broader context, every major lineage of lycophytes exhibits rooting systems derived from or incorporating downward growing stems or undifferentiated axes (Matsunaga & Tomescu, ).…”

Section: Introductionmentioning

confidence: 99%

Vascularization of the Selaginella rhizophore: anatomical fingerprints of polar auxin transport with implications for the deep fossil record

2017

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The Selaginella rhizophore is a unique and enigmatic organ whose homology with roots, shoots, or neither of the two remains unresolved. Nevertheless, rhizophore-like organs have been documented in several fossil lycophytes. Here we test the homology of these organs through comparisons with the architecture of rhizophore vascularization in Selaginella. We document rhizophore vascularization in nine Selaginella species using cleared whole-mounts and histological sectioning combined with three-dimensional reconstruction. Three patterns of rhizophore vascularization are present in Selaginella and each is comparable to those observed in rhizophore-like organs of fossil lycophytes. More compellingly, we found that all Selaginella species sampled exhibit tracheids that arc backward from the stem and side branch into the rhizophore base. This tracheid curvature is consistent with acropetal auxin transport previously documented in the rhizophore and is indicative of the redirection of basipetal auxin from the shoot into the rhizophore during development. The tracheid curvature observed in Selaginella rhizophores provides an anatomical fingerprint for the patterns of auxin flow that underpin rhizophore development. Similar tracheid geometry may be present and should be searched for in fossils to address rhizophore homology and the conservation of auxin-related developmental mechanisms from early stages of lycophyte evolution.

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