Integrative Morphological and Palynological Characterization of Cocos nucifera L.: Insights from Macro-Traits and Pollen Ultrastructure.

Coconut is popularly known as the "Tree of Life," yet precise germplasm characterization of aromatic varieties remains challenging due to the high phenotypic plasticity of vegetative and fruit traits. This study evaluated phenotypic and palynological variation among ten coconut varieties using an integrated multidimensional morphometric (MIM) approach that combined morpho-agronomic traits with scanning electron microscopy (SEM)-based pollen observations and multivariate analyses. Analysis of variance and genetic variability analysis indicated substantial variation in plant height, stem girth, and especially fruit weight (Hb2 = 0.97, GAM = 53.03%), suggesting that fruit weight may be a useful trait for further evaluation and selection within the studied collection. Pollen length (PL), width (PW), and pollen width-to-length ratio (PW/PL) did not differ significantly among varieties, indicating relatively limited variation in pollen dimensions within this collection. Polar length ranged from 33.82 to 44.55 μm, while the pollen width-to-length ratio (PW/PL), ranged from 1.06 to 1.37. Different pollen shapes, including navicular, reniform, ovoid, spherical, and subglobose forms, were observed within the examined samples. Multivariate analyses revealed variation among the varieties at both morphological and pollen levels. The agro-morphological-based PCA explained 74.4% of the total variation in the first two components and separated Var 10, Var 4, and Var 5 from several other varieties based on their combinations of vegetative, reproductive, and fruit-related traits. PCA based on pollen morphometrics explained 99.8% of the variation in the first two components, with pollen width, size index, and pollen length contributing strongly to varietal separation, particularly for Var 9 and Var 7. Qualitative pollen morphotype ordination further indicated differences in the distribution of pollen shape categories among varieties, while hierarchical clustering grouped varieties according to similarities in pollen dimensions and ratios, with Var 10 and Var 5 forming a group associated with relatively higher pollen width and size index values. These findings demonstrate that integrating morpho-agronomic and pollen-related characteristics can provide complementary information for characterizing variation within the evaluated coconut collection.