A reversal to hypogyny in Campanula alpina and its impact on capsule dehiscence: evidence from morpho-anatomy of the fruiting ovary

Abstract

Introduction. Campanula alpina is a perennial herbaceous bellflower grown in the Eastern Alps, Carpathians, and Balkans. Fruit in Campanula species opens by the hippocrepiform slits in the fruit wall, which are formed by axicorns, elongated structures inside the ovary composed of lignified parenchyma cells. Our objectives were to reveal the fruit structure and dehiscence mode in C. alpina and compare it with C. latifolia, a type species of the genus Campanula. Materials and methods. Flowers and fruits at different stages of morphogenesis of C. alpina subsp. alpina were examined. Plant materials were sampled in two plots in the Chornohora massif of the Ukrainian Carpathians. Results. Contrary to other Campanula species, in C. alpina only the basal part of the ovary is fused with the calyx forming the flattened ovary base. The placentation is axile, the fruit wall and septas are parenchymatous, only axicorns are lignified. Dehiscence of the hanged fruit proceeds by the curving of axicorns outside by drying. In the dehiscent capsule viewed from above, hollow openings in the horizontal ovary base are exposed, and the curved axicorns attached to the crumpled fragments of the ovary wall are visible inside the ovary. Discussion. The dehiscence of the fruit in C. alpina proceeds through septifragal and hippocrepiform slits like in C. latifolia. The main differences are that the ovary is mostly superior, openings are located on the horizontal ovary base, and valves together with axicorns curve inside the ovary. The semi-inferior or nearly superior ovary insertion could be traced in illustrations in digital databases and researches for some taxa of Campanula section Medium. No issues have been made on the evolution of the ovary position in Campanuleae, since only the inferior ovary was referred for this tribe before the present article. The functional implications of shifts in the ovary position in C. alpina could be a result of selection of the pollination mechanism, or dissemination mode. Conclusions. The peculiarity of the fruit in C. alpina is the axicorns curving inside the ovary during the dehiscence. It is expected that deviation from the inferior ovary will be confirmed in other related species of the Campanula with pendent fruits. No argumentation about the evolution of secondary hypogyny in Campanula has been proposed so far.