Characterisation of Phytolith Production and Their Taxonomic Use among Five Species of Aristida

: Phytoliths are amorphous silicon dioxide depositions in and around the cells of certain plants. Phytoliths of Poaceae are of great importance in the field of taxonomy and Archeology. Present study confirms the use of phytolith characters in the delimitation of Aristida species. Five species of Aristida were included in the study. Various characters like presence or absence of prickle hairs, nature of margins in lobate phytoliths, shank length in relation to the length of lobes etc. proved to be promising characters in the delimitation of the taxa. A taxonomic key to the identification of species is also provided.


INTRODUCTION
Phytoliths are silicon depositions in and around the cells of plants.Many plant families are known for their silica deposition.Members of family Poaceae are extensive producers of phytoliths.Phytoliths of Poaceae have been proved to be of great importance in taxonomy and archeology.Plants deposit silica in almost all the parts including roots, leaves, stem and inflorescence [1] [2] [3].Eventhough majority of the phytolith production occurs in the epidermal cells, subepidermal silicification is also common.The aim of the present study was to examine the pattern of phytolith production in five species of Aristida.The data may also be useful in archeological studies as it represents the complete foliar phytolith production in Aristida species.

MATERIALS AND METHODS
Herbarium specimens collected from Sivaji University Herbarium (SUK), and Calicut University Herbarium (CALI) were utilized for the present study.List of species studied is given in table 1. A. setacea Retz.11347 5.
A. stocksii (Hook.f.) Domin 1907 Phytoliths were studied in situ in epidermal peelings as well as in isolation.Isolation procedures and methods of peeling preparation used by Krishnan et al;2000 [4] were used for the present study.Phytoliths were photographed using Motic Digital Microscope.Measurements were taken using Motic Image Analysing Software.Various parameters considered were length, width, shank length and shank width.Frequency percentages of each morphotype were calculated by counting about 1000 phytoliths from each species.For measurements as well as frequency percentages, range, average and standard error are provided.Rules of International Code for Phytolith Nomenclature [5] were applied in naming and classifying the phytoliths.

DISCUSSION
Taxonomic potential of phytoliths in delimiting the taxa of the family Poaceae have been proved in many studies [4] [6] [7] [8].The present study aimed at revealing the variation of phytolith characters among 5 species of Aristida to be used in the taxonomic identification of the taxa.The different types of phytolith morphotypes, frequency percentages and pattern of arrangement of phytoliths in the epidermis were observed.Measurement of simple bilobates were taken to determine the potential of size parameters of phytoliths in delimitation of the taxa.Aristida was found to be an extensive phytolith producer with short cell silica bodies arranged in a tightly packed manner along the costal regions.The genus is characterized by the production of large sized bilobate forms with long or very long shanks according to the size based classification provided in our previous paper [7].Gallego & Distel (2004) [8] reported similar observations in A. subulata.Aristida being a species growing in sub arid regions, presence of long shanks and large sized phytoliths can be attributed to grasses growing in semi arid regions.However this can be generalized only through an extensive study of grasses including

Table 1 .
List of species included in the study

Table 2 .
Costal regions with 1-6 rows (more than 2 rows occasional) of bilobate simple types arranged with long axis parallel to the long axis of the leaf, closely packed in rows, interrupted at intervals and along costal margins by prickle-hairs (unciform type).Intercostal regions 55-85 µm wide, short cells rarely silicified, silica bodies elliptic or crescent-shaped, silicified micro-hairs and macro-hairs observed occasionally.(Fig.1.G&H) Adaxial epidermis: Prickle-hairs absent.All other characters are similar to abaxial epidermis.Voucher specimen: MAHARASHTRA: Osmanabad: Deobag, Potdar 1907 (SUK).Isolation studies Present study could reveal about 9 morphotypes of phytoliths in Aristida species.Morphotype and its abbreviation are shown in table2.Major classes of phytoliths and their abbreviation Frequency percentage of different morphotypes observed in each species is shown in table3.For each morphotype, abbreviation shown in the above table is used.Bilobate simple type (SB) followed by C, F or X represent the nature of margins.i.e.concave, flattened or convex respectively.Photographs of isolated phytoliths are provided in Figure2.Measurements of simple bilobates of each species is shown in Table4.

Table 3 :
Frequency percentage of the major classes of phytoliths (± S.E.) ISSN: