Phytolits of some mesomorphic species of bluegrasses (Poa L.) section Stenopoa and possibility of their use in systematics

Phytolits are the amorphous inclusions of a silicon dioxide. They can be found inleaves, interstices and glumes of many plants. Phytolits of grasses, being in most casescommon epidermal cells, impregnated with silicon, can serve for the diagnostic purposesin the same measure as the different taxa of grasses differ on a structure of epidermis.The purpose of our research was the specification of diagnostic value of phytoliths charactersfor bluegrasses systematics at specific and section level and an estimation of possibilityof using these characters for differentiation for morphologically close species.Three mesomorphic species of bluegrasses, belonging to closely related sectionsStenopoa (Poa palustris L. and P. nemoralis L.) and Tichopoa (P. compressa L.) havebeen investigated.The search of abaxial epidermis of 10 samplings (3-5 samples from each one) haven'trevealed essential anatomic distinctions among them. In costal zone all investigatedsamples had a pricles and hooks. The long cells of costal zone are narrower than ofintercostals zone, with parallel sinuous walls. Short cells are short and narrow, in pairor they may be solitary. The cells of intercostals zone are mainly long, but at some samplesthe special arrangement of long cells occurs: in the middle of intercostals zone thecells to be longer than in marginal part, and short cells and stomata appear. The stomataoccur in horizontal rows, usually 2 or 1 (between small veins). The walls of long cellsmay vary very much, from non-sinuous to markedly sinuous. The pricles may occur onthe leave margins as well.The search of phytolits has revealed their considerable variety both in form, and insizes. The search of epidermis allow to assume that they belong both to costal (more narrowand short cells) and intercostals (wide and long ones) areas. By origin the observedphytoliths represent the covering cells of epidermis, filled with silica, and trichomes, presentedby pricles and hooks of various shape and form. The observed covering cells ofepidermis as a whole belong to 4 types: 1) long cells with sinuous walls; 2) short cellswith sinuous walls; 3) long cells with non-sinuous walls; 4) short cells with non-sinuouswalls. Nevertheless, researches have shown the division to be quite relative and assuredthat a lot of intermediate forms between these 4 types occur. All observed phytoliths arecharacteristic for festucoid grasses. The marked difference in phytoliths of P. palustris,P. nemoralis, and P. compressa and sections Stenopoa and Tichopoa as well, has notbeen not revealed, and, in spite of they being significant variable, the unique form, characteristiconly for one of the investigated sections or species has not been found. Thus,the authors regard the phytoliths characters as being of limited taxanomical value, butthese data can be used for identification of phitoliths, isolated from fossils.

Keywords

Authors

References