The False Leaf-Sheath Homology of the Coleoptile Results from an Optional Morphological Embryo Axis, Not from Ontogeny: A Response to Scanlon et al. (2026)

<jats:p>Counter-arguing against the proposition that homology between the coleoptile and the leaf sheath is impossible because a sheath cannot be located above the lamina of the same leaf (Mavrodiev 2025), while defending the bipartite interpretation of the grass cotyledon (BIGC), Scanlon et al. (2026) advance five principal objections: (1) during embryo ontogeny, the coleoptile initiates proximal to the initiation point of the distal scutellum; (2) the coleoptile must be part of the cotyledon because of embryo distichy; (3) tissue continuity between the scutellum and coleoptile supports the interpretation that these two structures together constitute a single composite organ, the cotyledon; (4) BOP1a marker expression in coleoptile supports coleoptile-sheath homology; and (5) ligule and leaf-sheath homologies of the coleoptile are compatible because the ligule represents an extension of the sheath margin. In this reply, I show that all five objections are incorrect. (1) Along the embryo's morphological axis, rather than the proximodistal axis of the leaf, the coleoptile occupies a position distal relative to the scutellum, thus lying above the latter. Therefore, homology between the coleoptile and the leaf sheath is impossible. (2) The disruption of embryonic distichous phyllotaxy by the placement of the coleoptile does not necessarily constitute a morphological argument, and the interpretation of the epiblast as a reduced leaf preserves embryo distichy. (3) Tissue continuity does not imply organ identity. (4) BOP1a expression in coleoptile provides evidence against, rather than in support of the BIGC. (5) Coleoptile-leaf sheath homology does not constitute evidence for coleoptile-ligule homology (or vice versa). Moreover, the claim that the ligule originates from the sheath margin remains open to question because it is formulated without consideration of the basipetal pattern of maize leaf maturation. The reply to Objection 1 affects the very foundation of the argument of Scanlon et al. (2026). Therefore, further discussion on the topic is optional (sublato fundamento, cadit tota propositio).</jats:p>