Stable isotope composition (d 13 C and d18 O) was analysed in mineral incrustation of Chara rudis and surrounding waters. This macroalga forms dense and extensive charophyte meadows and may significantly contribute to the calcium carbonate precipitation and deposition of marl lake sediments. The study aimed to find out if charophyte calcium carbonate was precipitated in an isotopic equilibrium with lake water and if the precipitation was related to the environmental conditions. Two apical internodes of 10 individuals of C. rudis were collected monthly between June and late October 2008 at three permanent study sites (1.0 m, 1.5 m and 2.0 m deep) in a small (15.1 ha) and shallow (mean depth: 4.3 m) mid-forest lake with extensively developed charophyte meadows (Lake Jasne, mid-Western Poland). Basic physical-chemical analyses were performed at each study site, and water samples for further laboratory determinations, including stable isotope analyses, were collected from the above searched C. rudis stands and, simultaneously, at three comparative sites in the macrophyte-free pelagial. The difference in d 13 C between incrustation and water from above C. rudis exceeded 2% V-PDB at each site. In the case of d 18 O, it exceeded 2% between July and September. Accordingly, it is postulated that calcium carbonate was not precipitated in an isotopic equilibrium with lake water. Incrustation was enriched in heavier carbon isotope, 13 C, and water was enriched in 18 O. d 13 C of incrustation and DIC were positively correlated, whereas negative relation 18 O of incrustation and water. Several dependencies were found with water chemistry above the plants. The content of mineral incrustation in Chara dry weight had negative influence on the d 18 O but not on the d 13 C. Community depth, structure and PVI had no effect. No significant differences appeared between isotope composition in the pelagic zone and Chara stands.

Morphological features of oospores of Chara baueri A. Braun, one of the rarest charophyte species worldwide, were studied based on 100 oospores collected from a small and temporarily dried mid-field pond near Cedynia, Western Poland. This is the first Polish and fifth presently known locality of this species. For comparison 67 oospores from a German population (similar pond localized near Batzlow, Germany) were also measured. So far, data on morphology of C. baueri oospores as well as the species ecology are limited. The only more detailed study of oospores for this species was earlier performed on 15 oospores from Kazakhstan. Largest polar axis (LPA, length), largest equatorial diameter (LED, width), isopolarity index (ISI = LPA/LED × 100), number of ridges, width of fossa, distance from apical pole to LED (AND) and anisipolarity index (ANI = AND/LPA × 100) were measured. The comparative analysis revealed that the oospores from Poland are generally bigger and more prolate than the Ger­man ones. The differences for most of studied parameters were statistically significant. The finding is discussed in the context of habitat differentiation of both studied sites. Moreover, the results obtained of oospore measurements for both populations differs from most of the data known so far from the literature

Morphological features of oospores of a rarely noted species Chara braunii Gmel. were examined in a local population (fishpond near Tuplice village, Ziemia Lubuska region, mid-western Poland). The largest polar axis (LPA, length), largest equatorial diameter (LED, width), isopolarity index (ISI = LPA/LED* 100), and the number of ridges and width of fossa of 90 oospores were measured. Additionally, the oospore wall ornamentation pattern was examined by means of scanning electron microscopy (SEM). As a result, a cylindrical shape and the lack of so-called “shoulder” were found. Oospore length and width ranged between 466.8–600.1 µm and 250.1–366.7 µm, respectively, with the ISI index values between 148 and 213. The number of ridges was 8–10 and the width of fossa varied between 50.0 and 66.7 µm. The oospore width appeared to be the most changeable feature, whereas, by contrast, the number of ridges was the least variable character. Wall ornamentation can be described as tuberculate and a ribbon was present on the ridges. As a comparative material for the study performed, 9 oospores from Professor Izabela Dąmbska’s Collection of Charophytes of Poland were measured. It was evidenced that variation ranges of most of the features of Chara braunii oospores from Tuplice fishpond are similar to those of Professor Dąmbska’s herbarium materials and to data reported by authors from other countries as well. The morphology of reproductive structures does not follow the variation of thalli characteristics.