Variation In Rhododendron Calendulaceum Germination Behavior Influenced by Seed Morphology and Site Specific Characteristics

Rhododendron calendulaceum, a species endemic to the Appalachian mountain region of the Eastern U.S., is a species of horticultural and ecological significance. In the wild, this species exhibits a high degree of inter- and intra-population variation in morphological and physiological characteristics. Inherent differences among populations suggest that variations in germination behavior may exist in wild collected seeds.  Investigation of the seed and site specific characteristics separating existing populations can potentially lead to an identification of a particular native seed source suitable for widespread propagation, and aid in the development of ecological preservation protocols. Our objectives were twofold: 1) investigate morphological and environmental differences through seed and site analyses to accurately gauge the influence of seed size parameters and environmental factors on germination behavior, and 2) conduct standard germination studies, including cold stratification, and identify variation in germination characteristics according to seed source. Eight separate wild collected sources of R. calendulaceum seeds were used in this study. Variation in overall seed and embryo parameters within and among sources were identified. Significant differences in germination percentages existed between collections, with values ranging from 39.8% to 74.6% in non-stratified seeds, and 50.7% to 76.3% in seeds subjected to cold stratification. Significant differences existed between T₅₀ and T_10-90 values among seed source collections, with seed size being highly correlated with germination uniformity (T_10-90). Cold stratification showed no significant improvement of overall germination percentages in the sources tested. Our findings demonstrate that germination behavior differs greatly between seed source locations, impacted by seed size parameters, and site specific environmental factors.