Morphological and taxonomical treatments of fruits in the subclass Rosidae Takht. of the flora of Ukraine

Abstract

Introduction. Rosids is the pivotal clade of eudicots, whose taxonomic composition was significantly changed based on molecular phylogeny. Molecular insight led to the re-evaluation of many phenotypic features, especially in reproductive morpho­logy. Although the floral structure and evolution within the current scope of rosids were actively investigated, the morphological structure of fruit was almost fully neglected. The present study aimed to survey the morphological diversity of fruits in rosids (subclass Rosidae) in the flora of Ukraine to reveal the most common fruit types, analyze the distribution of the basic fruit types among rosids, and survey some comparative-morphological features of gynoecium and fruit. Materials and Methods. Fruit features have been surveyed based on many carpological sources. We also analyzed the gynoecium characteristics crucial for fruit deve­lop­ment, i.e., the type of ovary insertion, placentation, and ovule and locule number. For Rosidae, seven basic fruit types were recognized using the approach previously elaborated for the monocot plants of Ukraine: aggregate fruit, multi-seeded monocarp, capsule, berry, multi-seeded pyrenarium, schizocarp, and one-seeded fruit. Results. As a result, the annotated list of morphological characteristics for each of the 54 families of Rosidae occurring in Ukraine was composed. In this list, the complementary and the most contrasting definitions of fruits from different sources were combined. Discussion. According to our calculations, the subclass Rosidae in the flora of Ukraine is represented by 326 genera and at least 1617 species. Our results demon­strated that the most widespread fruit types at the family level seem to be capsular and one-seeded fruits, while at genus and species level the portion of multi-seeded monocarps and aggregate fruits is also significant. Nine families reveal more than one basic fruit type in the flora of Ukraine. Some fruits are ambiguously classified into one or another fruit type because of their intermediate features. Thus, fuzzy boundaries between most fruit types are evident. Conclusions. The obtained results have been compared with our previously reported results for the monocot clade in the flora of Ukraine. In both cases, the predominance of capsular fruits at the family-level spectrum of basic fruit types was clearly demonstrated. The results of our analysis suggest that the model of basic fruit types has the potential to be applied to the formal treatment of fruit structure in other groups of angiosperms.