4.1 Umbel development
The development of umbels is not unknown subject in Apiaceae. Many of them, however, have studied by light microscopy (Payer 1853, 1857, Jochmann 1854, Sieler 1870, Schuchardt 1881, Schumann 1890, Jurica 1922, Borthwick et al. 1931, Sattler 1973) and less by scanning electron microscopy (e.g., Erbar and Leins 1985, Bull-Hereñu and Claßen-Bockhoff 2010, 2013, Claßen-Bockhoff 2016, Baczyński et al. 2022). In Da. carota , Chaerophyllum temulum L., and Pastinaca sativaL., the umbel meristems fractionated acropetally umbellets. In Da. carota , the presence or absence of terminal flower in umbellets depends on nourishment conditions that, in turn, directly effects on geometry of apical meristems. Thereby, the weaker plants produce flat “open” umbellets lacking terminal flowers whereas the vigorous plants with dome-shaped “closed” umbellets initiating terminal flowers with pedicels. The obligate “closed” umbellets in Ch. temulum and “open” in P. sativa produced dome-shaped and flat umbellet meristems, resulting in presence and absence of terminal flowers, respectively (Bull-Hereñu and Claßen-Bockhoff 2010). In Di. persica, dome-shaped umbellets are similar to those “closed” umbellets bearing perfect flowers that is likely related to its habitat and annual habit form. This species occurs in lowland savanna-like vegetation that dominated with shrubby species like Acacia ehrenbergiana Hayne and Ziziphus spina-cristi (L.) Desf.Its short vegetation period coupled with annual habit form, low annual precipitation and environmental conditions like poor soils and exposing in warm wind and extreme sun radiation. The annual habit form obliged the plant to complete its life cycle in a short time. Moreover, the severe environmental factors may likely adopted the plant to set one perfect flower within umbellet. The unique “cage-like” umbellets, therefore, likely linked with habitat conditions and annuls habit form.