The specific features of the reproductive biology of the rare species Gueldenstaedtia monophilla Fisch. (Fabaceae)

The seed production of the rare species Gueldenstaedtia monophylla has been investigated in 19 coenotic populations in the territories of Russia (Central Altai) and Mongolia (the north-western part). G. monophylla reproduces exclusively by seeds and is characterized by the low number and density of the plants in the populations. Its populations have a high proportion of generative plants: from 31 to 84% from the total number of the plants. The plants of G. monophylla have a small number of generative shoots, varying from 1 to 6 per plant. The number of flowers on the plants is low, too, and varies in the populations on average from 1.2 to 15.3 per plant. The potential seed production (PSP) varies considerably from 13.5 to 308.6 ovules per plant. The real seed production is much lower, to constitute from 6.2 to 74.5 seeds per plant. The low seed production, fructification that occurs not every year, and scanty populations make the species vulnerable.

species are in the focus of most studies referring to rare species and to revealing their specific characteristics [8,9].
The purpose of this study was to investigate the seed production of G. monophylla.

Materials and methods
19 coenotic populations (CP) of G. monophylla have been investigated. The studies were conducted during the vegetation seasons of 2005-2016 in the territory of Russia (western Siberia, Central Altay) and north-western Mongolia.
In each population, 25-30 plants of the middle generative age were investigated. The following parameters of seed production were considered: the number of generative shoots per plant, the number of inflorescences, the number of flowers in an inflorescence, the number of beans, and the number of ovules and seeds per bean. To characterize seed production, the following parameters were determined: potential seed production (PSP), real seed production (RSP), and the percentage of semenification (PS), showing the ratio of RSP and PSP [10].

Results and discussion
Gueldenstaedtia monophilla is a perennial grassy taproot plant with polycarpic shoots of a rosette type, incapable of vegetative reproduction. Thus, seed preproduction is the only way of reproduction and spread of this species. G. monophilla is a cross-pollinating species, it blossoms in May-June, and produces fruits in June-July. The beans are 2 -3 cm long, and have a linear and cylindrical shape.
As a rule, the populations are not numerous (50 -2000 plants), fragmented and have low density of the plants [11]. In the CPs investigated, the percentage of generative plants was 31-84% from the total number of plants in the population [12]. Fruits do not set every year on generative plants: there are cases when beans do not form on a plant during one year or several years. Breaks in fruit-bearing are related to the unfavorable conditions of the vegetation periods in some years, draughts and recurring frosts. The percentage of generative plants which did not set fruits in the population may reach 100% of the total number of generative plants, thus making a significant contribution in the total seed production. The number of non-fruit-bearing plants varies considerably in different years of study and may constitute from several plants to practically all the generative plants in individual populations. For example, in 2006, the percentage of the plants which did not form fruits varied from 12.5% (CP Bolshoy Yaloman) to 69% (CP Chuy-Oozy), on average for populations, 35.4%. In 2010, the share of plants which did not set fruits in CP Maly Yaloman was 60%, and in CP Malaya Inya, it was 70%.
The plants G. monophilla form a small number of generative shoots from 1 to 6 per plant (Table).  (Table).
The seeds of G. monophilla have a rounded kidney shape and colored light-beige and greenish-beige; the surface of the seeds is matte and without pubescence. The size of the seeds was on average 2.98±0.03 mm long and 2.62±0.04 mm wide. The mean weight of the seeds differed among the populations more than two times, to constitute from 0.28±0.02 to 0.77±0.03 g (100 seeds). Based on this sign, the populations under study may be conditionally divided into the following groups: populations in which the plants have seeds having low, medium and high weight. All the populations except one were found to belong to two groups, with seeds of high and low weight. Eight CPs (47.4%) out of 19 had low weight of the seeds, varying from 0.28 to 0.43 g, the lowest average seed weight was recorded in CP Inegen 2 (0.28 g) and Malaya Inya (0.30 g). The high weight of the seeds from 0.61 to 0.77 g was found in 10 CPs (52.6%), with the highest seed weight recorded in CPs Bolshoy Yaloman and Saldzhar -0.77 g. And only one CP, Nizhny Inegen, may be referred to the middle group with the middle weight of the seeds, 0.54 g. In the investigated coenopopulations of G. monophilla, significant variation in the parameters of seed production has been revealed. Potential seed production (PSP) far exceeds the real seed production. Essential variations in PSP have been revealed not only among the populations but also in different years of the study (Fig. 1). In CP Chuy-Oozy, PSP varied from 17.6 to 40.9 in different years of observations. Maximum PSP was observed in the populations from Mongolia: 116.5 -308.6, on average being 195.6. In the populations of Mountainous Altay, PSP was found to be much lower, to constitute from 13.5 (CP Bolshoy Ilgumen 2010) to 87.8 (CP Inegen 2006), being on average 39.3.
The real seed production (RSP) varied from 6.2 to 74.5%. The lowest RSP, 5.5 and 6.2%, was found in CP Chuy-Oozy 5 (2010) and Bolshoy Ilgumen (2010). This is related to the small number of generative shoots on a plant, totaling on average 1.0, and to the small number of ovules developing into seeds. The highest RSP was recorded in CPs from Mongolia Hovd 2 and Hovd 3 -74. 5