Analysis of Floral Trait Diversity and Its Correlation with Fertility in Hibiscus syriacus Cultivars

Hibiscus syriacus L. is a landscape plant with ornamental, economic, and ecological value. However, the low natural fruit-setting rate observed in most cultivars significantly hinders its crossbreeding, germplasm innovation, and large-scale application. We analyzed 20 cultivars to identify the key floral traits associated with H. syriacus fertility. Fifty floral phenotypic and pollen morphological indicators were systematically quantified, fruit-setting and pollen vitality rates were recorded, and insect foraging behaviors were observed to assess the diversity of floral characteristics and their correlation with fertility. The results showed that notable variations in floral phenotype and pollen morphology exist among the studied cultivars. Pollen grains were characterized by spinous ornamentation, with notable differences in grain size, spine morphology, and surface wrinkling. Correlation analysis identified nine core floral and palynological indicators that are highly associated with H. syriacus fertility. These comprise five floral phenotypic variables, such as pistil length (PL2) and heart length (HL), and four microscopic palynological features, including thorn curvature (TC) and spine number (TN). We built a phenotypic and palynological framework for analyzing fruit setting in H. syriacus. These nine key traits can act as morphological markers to quickly assess hybrid parents, supporting its genetic improvement, breeding and industrial promotion.