Structural and elemental characterization of hull, seed coat, and cotyledons in developing peanut seeds.

Peanuts (Arachis hypogaea L.) seed tissues differ in structure and function, yet their surface morphology, internal anatomy, and elemental composition during development have not been examined in a combined microscopy framework. Seeds of three runner-type cultivars, Georgia-06G (G-06), Georgia-12Y (G-12Y), and Georgia-18RU (G-18) were sampled across reproductive stages R3-R8 and analyzed using histology, scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS). SEM and histology revealed hull sclerenchyma, cotyledonary parenchyma, and distinct outer-inner surface variations in both hull and seed coat. Inner cotyledon stomata were classified as anomocytic, anisocytic, and paracytic. Elemental analysis indicated non-uniform calcium (Ca) and silicon (Si) distributions across tissues and stages. Outer hull Si ranged from 2.50 to 9.97 wt concentration percentage (wt%); inner hull Si remained below 0.5 wt%, except for G-06 at R3 (1.86 wt%). Outer hull Ca peaked early and declined with maturity; G-18 reached 4.95 wt% at R3, approximately 3.6- to 3.8-fold higher than other cultivars. Inner hull Ca reached 3.48 wt% in G-12Y at R3. Seed coat Ca and Si were consistently lower, remaining below 0.85 wt% and 0.51 wt%, respectively. EDS data are semi-quantitative and biological replication was not included; results are presented descriptively. These findings support a layered structural and elemental barrier organization in peanut reproductive tissues.