Andromonoecy of Aegopodium podagraria (Apiaceae) in Moscow region

In Apiaceae, hermaphroditism and andromonoecy are the most common sexual systems, especially in the northern hemisphere. The available literature contains little information about the structure of synflorescences in Aegopodium podagraria L. and the peculiarities of its sexual expression. The main aim of our research was to identify the sexual differentiation in perennial rhizomatous herb A. podagraria. We observed natural populations near Pavlovskaya Sloboda village (Moscow region, 55°48'52''N, 37°05'16''E) in 2016 and 2017. We used standardised terminology and designation system for all umbels within the synflorescence in Apiaceae representatives [Kuznetzova TV and Timonin AC, 2017]: simple umbel; compound or double umbel composed of simple umbels; terminal double umbel ending the main shoot. We studied the structure of synflorescences in 50 A. podagraria individuals selected at random. For that, we investigated 50 terminal umbels, 100 umbels on shoots of the second order of branching and 50 umbels on shoots of the third order of branching. 8 quantitative traits of each individual characterizing the structure of umbels and umbellets were studied. The degree of andromonoecy was calculated as the percentage of staminate flowers in the terminal umbel and in one representative umbel of each shoot of different orders. The morphological features in 25 different individuals of 100 perfect flowers in terminal umbels, 100 perfect flowers in umbels on shoots of the second order and 200 staminate flowers in the umbels on shoots of the second and third orders of branching were analysed. 11 quantitative traits of each individual characterizing the structure of flowers of different sex types on shoots of different orders were studied. The sizes of flower parts were measured using a stereoscopic microscope with an eyepiece micrometre with ×20 or ×40 magnification depending on the size of the measured organ. The morphology of the flowers was described according to the “Atlas.......” [AlA Fedorov and ZT Artyushenko, 1975]. To determine the quality of pollen, we used the method of acetocarmine staining. The sizes of pollen grains and the quality of pollen from perfect and staminate flowers were analysed according to three quantitative traits in 50 different individuals selected at random. To produce pollen, 5 most mature anthers from each flower were used. For each individual, we took 5 flowers from different parts of double umbels located on shoots of different orders. The pollen was studied under the microscope with magnification of 16×10. Pollen grains were counted in 30 fields of view. 300-500 pollen grains were examined in each flower. In total, we studied pollen of 250 perfect flowers in terminal double umbels, 250 perfect flowers in double umbels on shoots of the second order of branching and 500 staminate flowers in double umbels on shoots of the second and third orders of branching in 50 different individuals. The pollen of perfect and staminate flowers was studied according to 3 characteristics: equatorial diameter and polar axis of fertile pollen grains, μm, and pollen fertility, %. We found that the main flowering units of A. podagraria are compound umbels that are composed of umbellets. Our data allow us to determine that synflorescences of A. podagraria are racemes or panicles composed of compound umbels. According to our records, the remaining branches repeat the pattern of the main axis and produce lateral umbels up to the third order. Umbellets in A. podagraria can have terminal flowers (in large and branched individuals) or lack terminal flowers (in unbranched individuals). The compound umbels can be terminal and lateral. We showed that up to 8 compound umbels are produced per individual. The umbels bear 18-25 umbellets with 4-32 flowers each. We conclude that a clear size gradient is observed between the umbels. The terminal umbel is dominant. Terminal umbels [0 10-11 cm] are always bigger than lateral umbels [0 3-7 cm] of the second and third orders of branching (See Table 1). Individuals are clearly andromonoecious, producing up to 4000 flowers with 20% of them being staminate. Umbellets can have marginal hermaphrodite flowers and central staminate flowers. Staminate sterile flowers are located in the centre of the umbellets and more frequently in the inner umbellets of an umbel. Finally, our results suggest that with the increasing order of branching the number of outer perfect flowers declines and the proportion of staminate flowers increases leading to completely staminate umbellets in the centre of the umbels and to completely (functionally) staminate umbels in the highest order of branching. In this research, we established that two types of flowers (hermaphrodite and staminate) are clearly different in structure and size. Both types of flowers are zygomorphic, cyclic and 4-circular, with double perianth. The gynoecium of hermaphrodite flowers is bicarpelate and united, two styles that are fused at their base forming a nectarsecreting disc (stylopodium). In staminate flowers, we registered a total reduction of styles and carpels except for stylopodium that produces nectar. Perfect flowers and their parts are bigger than staminate flowers except for the size of anthers that are equal in those types of flowers (See Table 2). We found that the sizes of hermaphrodite flowers and their parts (except for the sizes of anthers and pollen fertility) regularly decrease in the direction from terminal double umbels to double umbels on shoots of the second and third order of branching. A similar situation is observed in staminate flowers located in double umbels along shoots of the second and third order of branching. We assumed that the differences in degree of nutrient availability determine the size differences of hermaphrodite and staminate flowers, which are located in different position of umbellets in the composition of double umbels on a shoot of the same order of branching and in double umbels on shoots of different orders of branching. The paper contains 2 Tables and 25 References.

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