Seed Dimension and Weight of Selected Rubus Species

Abstract

Many lesser-known wild Rubus species from Ecuador, the People's Republic of China, and North America have been obtained on recent U.S. Dept. of Agriculture plant-collecting expeditions. In this study, the seed size of 43 Rubus species was measured. An 80-fold range in seed weight was observed within the genus. Asian species in the subgenera Idaeobatus and Malachobatus had the lightest seed, ranging from 0.3 mg (R. eustephanus Focke ex Diels) to 1.2 mg (R. coreanus Miq.). The seeds of ≈80% of the species examined weighed <2 mg. Seeds of European species in the subgenera Idaeobatus and Rubus (formerly Eubatus of Focke) ranged from 1.3 to 3.0 mg. The South American Orobatus included several of the heaviest-seeded species. Rubus megalococcus Focke (subgenus Rubus) had the heaviest and largest seed weighing 24.2 mg. Seed weight was not related to ploidy level in wild species. Seed weight and length were positively correlated. Seed flatness was not related to seed length. Several of the smaller-seeded Asian species, such as R. minusculus A. Lev. & Van., R. hirsutus Thunb., and R. eustephanus, had more drupelets per fruit than did those of larger-seeded species. This heritable trait may be useful in breeding for increased fruit size.