Anther glands in Mimosoideae (Leguminosae) are emergences with a conserved meristematic origin

- Ontogeny is used to understand the morphological diversity of anther glands.
- Glands arise from divisions in the first three cell layers of the young anther.
- The origin from epidermal and underlying tissue characterizes them as emergences.
- Data indicate a conserved meristematic origin of anther glands in Mimosoideae.

The six distinct gland types described in Mimosoideae anthers vary from simple projections to robust and vascularized structures. The origin of these glands is attributed to an extension of connective. However, except for an illustrative recording of some developmental stages, nothing is known about the origin and gland development, which prevents their correct classification. This study aimed to elucidate the ontogeny of four of the six gland types detected in the anthers of Mimosoideae. The intention was to understand whether the morphological diversity results from different ontogenetic processes. For this, flower buds of various sizes of four Mimosoideae species with different types of glands were collected: Stryphnodendron adstringens (Piptadenia subtype Piptadenia), Tetrapleura tetraptera (Piptadenia subtype Adenanthera), Adenanthera pavonina (Piptadenia subtype Entada), and Pentaclethra macroloba (Pentaclethra type). The samples were processed for surface (scanning electron microscopy) and anatomical analyses (light microscopy). Despite their morphological differences, the glands share a common meristematic origin. They arise from simultaneous divisions in the first three layers of meristematic cells that cover the apical portion of the young anther. After the formation of the protuberance, the developing glands undergo different specialized processes that include (1) elongation of the epidermal cells in Piptadenia subtype Adenanthera and Piptadenia subtype Entada, (2) degradation of central gland cells in Piptadenia subtype Entada, (3) change from a rounded to a triangular shape in the Pentaclethra type, and (4) cell differentiation into a procambial meristem and subsequently into vascular tissue in the Pentaclethra type, resulting in the diversity encountered in the group. Their origin from protodermal and fundamental meristem cells characterizes the anther glands as emergences. Our data indicate a conserved meristematic origin of glands, favoring the hypothesis of homology of these structures and supporting the monophyly of the Mimosoideae clade.