Comparative studies on ovule development in Lardizabalaceae (Ranunculales)

•We used SEM and LM to investigate ovule morphogenesis of 5 genera in Lardizabalaceae.•The developmental features are variety in the family.•Cup-shaped inner integument with annular initiation and hood-shaped outer integument with semi-annular initiation are the basic type.•Cup-shaped outer integument developed from semi-annular initiation (in Sargentodoxa) is derivative features.

Ovules development and structure of 6 species of 5 genera in Lardizabalaceae were studied under SEM and LM. Ovule morphology show diversity in the family: anatropous (Sinofranchetia and Decaisnea) or campylotropous (Sargentodoxa, Akebia and Holboellia); ovule number is 1 (Sargentodoxa) to 20 (even up to 180 in Akebia and Holboellia); mature ovule size is from 150 μm (Holboellia) to 350 μm (Sinofranchetia and Sargentodoxa) in length; placenta marginal or laminar-diffuse; bistomic or endostomic, in Decaisnea, the micropyle is formed by inner integument only; and the thickness of outer integument is vary from 2 to 3 to 5–6 cell layers (Decaisnea). Akebia and Holboellia had secretory hairs surrounding ovules. While, morphological features common to all species included (1) bitegmic integument, cup-shaped inner integument (consists of 2–3 cell layers) derived from an annular ring, and hood-shaped outer integument developed from semi-annular initiation (except Sargentodoxa, the cup-shaped outer integument with semi-annular initiation); (2) inner integument initiated at the stage of sporogenous cell or megaspore mother cell, while outer integument formed later; (3) crassinucellar, the megaspore mother cell 3–6 cell layer deep within the nucellus; (4) the short funiculus, a vascular bundle reached to the chalazal pole region connecting ovule to placenta, and no funiculus appendage was found.

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