Phytoliths of pteridophytes

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1 South African Journal of Botany 77 (2011) Minireview Phytoliths of pteridophytes J. Mazumdar UGC Centre for Advanced Study, Department of Botany, The University of Burdwan, Burdwan , India Received 3 June 2010; received in revised form 14 July 2010; accepted 28 July 2010 Abstract Study of phytoliths of pteridophytes is an emerging area of research. Literature on this aspect is limited but increasing. Some recent findings have shown that phytoliths may have systematic and phylogenetic utility in pteridophytes. Phytoliths are functionally significant for the development and survival of pteridophytes. Experiments with some pteridophytes have revealed various aspects of silica uptake, deposition and biological effects SAAB. Published by Elsevier B.V. All rights reserved. Keywords: Biogenic silica; Ferns; Pteridophytes; Phytolith; Silicification 1. Introduction Many plants deposit silica as solid hydrated Silicone dioxide (SiO 2,nH 2 O) in the cell lumen or in intercellular spaces, where it is known as phytoliths or plant stones (Greek, phyto = plant, lithos = stone) or silicophytoliths or opal phytoliths or plant opal or opaline silica or biogenic silica or bioliths. The term phytolith may also be applied to other mineral structures of plant origin, including calcium oxalate crystals, but is more usually restricted to silica particles (Prychid et al., 2004). Phytoliths are extremely durable in the soil and may not migrate through it to the same extent as do other microfossils, such as pollen and diatoms (Prychid et al., 2004). Many plants produce phytoliths with characteristic, distinguishable shapes, and which are known accordingly as diagnostic phytoliths. Diagnostic phytoliths recovered from soil provide valuable information about the identity and possibly concentration of source plant species, and are useful for the reconstruction of palaeoenvironments, investigation of ancient agricultural practices, study of crop plant evolution, monitoring vegetation and climate change, radiometric dating, identification of drug plants, crop processing (Harvey and Fuller, 2005), forensic investigations, indicator of diets of ancient animals (more discussion in Prychild et al., 2004; Piperno, 2006 and citations therein), and recently for nanotechnology (Neethirajan et al., 2009). address: jaideepmazumdar10@gmail.com. In spite of environmental effects on silica uptake, ongoing investigations indicate that phytolith formation is primarily under genetic control (Piperno, 2006). Phytoliths have been used successfully as taxonomic tools in angiosperms, especially in monocots (Piperno, 1988; Tubb et al., 1993). Less information is available about pteridophytic phytoliths. The objective of this review is to evaluate the present status and future prospects of phytolith research in pteridophytes. 2. Phytoliths in pteridophytes The umbrella terms pteridophytes and ferns and fern allies were used to denote a group of spore bearing, seed-less vascular plants that demonstrated many aspects of early evolution of land plants and undergone considerable taxonomic treatments. Based on morphological and molecular data Lycopods or Lycopsids, previously placed in fern allies are now separated as clade Lycophytes sister to all other land plants and Whisk ferns and Horsetail, also previously considered under fern allies are now included within Ferns or Monilophytes or Moniloformopses (cf. Smith et al., 2006). In a recent treatment Chase and Reveal (2009) recognized Lycophytes as Subclass Lycopodiidae Beketov and placed 5 subclasses Subclass Equisetidae Warm., Subclass Marattiidae Klinge, Subclass Ophioglossidae Klinge, Subclass Polypodiidae Cronquist, and Subclass Psilotidae Reveal under Monilophytes. However, in the present account term /$ - see front matter 2010 SAAB. Published by Elsevier B.V. All rights reserved. doi: /j.sajb

2 J. Mazumdar / South African Journal of Botany 77 (2011) Fig. 1. Phyoliths of Huperzia selago (A), Blechnum orientale (B), Vittaria himalayaensis (C), Equisetum diffusum (D) and Selaginella bryopteris (E). (Bar in A=100 μm, in B, C and D =20 μm, in E=10 μm). pteridophytes is used in broad sense, encompassing all clades of Ferns and Lycophytes. Davy (1814) was one of the first to investigate the form of silica in plants, including the epidermis of Equisetum, and Mettenius (1864) coined the terms Deckzellen (cover cells) or Stegmata (from the Greek stegium, a roof or covering) for cells that contain inclusions and lie over sclerenchyma in ferns; these cells contained calcium oxalate crystals in Cyatheaceae, silica concretions in Dryopteris and true stegmata (cells containing silica bodies) in most Trichomanes species (cf. Prychid et al., 2004). In pteridophytes silica bodies in different plant parts have been observed by several authors, including Mettenius (1864), Pant and Srivastava (1961), Kaufman et al. (1971), Dengler and Lin (1980), Parry et al. (1985), Rolleri et al. (1987), Piperno (1988), Le Coq et al. (1991), Lanning and Eleuterius (1994), Stevenson and Loconte (1996), Thorn (2006) and others (cited by Sundue, 2009). However, distinguishable forms or diagnostic forms of silica bodies or phytoliths, useful for delineation of family, genus or species are known for only few taxa (Table 2). Mazumdar and Mukhopadhyay (2009a,b, 2010) surveyed 47 species of pteridophytes and suggested that phytoliths could be useful for taxonomic purposes as some plate or sheet-like phytoliths show distinct features in different species. Using scanning electron microscope Page (1972) made detailed observations on surface micromorphology of silicified aerial shoots of Equisetum and proposed three sections under Subgenus Equisetum Section I: Equisetum sect. nov. (contains E. fluviatile and E. arvense), Section 2: Subvernalia A.Br. (contains E. pratense and E. sylvaticum) and Section 3: Palustria sect. nov. (contains E. bogotense, E. diffusum, E. palustre and E. telmateia) on the basis of variability of shape, size and distribution of pilulae (bead like projections), mamillae (rounded or conical projections) and stomatal cell area (paired cells around each stomatal pore). He also noted variations among silica deposition patterns in Subgenus Hippochaete (smooth or amorphous type depositions) and Sebgenus Equisetum (granular type depositions). But, Hauke (1974) considered that the available information was insufficient to formulate a sectional classification of the subgenus Equisetum (cf. Guillon, 2004) and this treatment was not accepted widely. However, variations in surface micromorphological features among different species of Equisetum indicated their possible use for identification at species level. Filippini et al. (1995) utilized micromorphological features like, size of mamillae and pilulae distribution over the surface of stomata for identification of E. arvense in finely powdered form of commercially available drug Herba equiseti. Sundue (2009) studied epidermal phytoliths from leaves of ferns belonging to Family Pteridaceae sensu Schuettpelz et al. (2007). The occurrence of phytoliths were found to be a potential synapomorphy for the adiantoid clade, several smaller clades of pteridoid clade, including Pityrogramma and the sister group of Actiniopteris and Onychium. Phytoliths were not found in Ceratopteridoid or cryptogrammatoid clades. But phytoliths were diagnostic in adiantoid and pteridoid clades (Table 2) and diverse in cheilanthoid clade, reflecting independent origins of these major lineages. This study also indicated that phytoliths were evolved once in adiantoid and twice in pteridoid clades. But this analysis was scored by two characters (presence/ absence and location of phytoliths) and use of morphological features like shape, margin, and surface ornamentations of phytoliths might provide better resolution of interrelationships of clades. Although this study reported the absence of phytoliths in Pteris vittata, they were found in lamina and vein area in pinnule by Chauhan et al. (2009). Also, more sampling is required for Ceratopteridoid and cryptogrammatoid ferns to confirm the absence of phytoliths in these clades. For extraction of phytoliths from plant tissues Chauhan et al. (2009) used dry ashing method in which samples were heated in

3 12 J. Mazumdar / South African Journal of Botany 77 (2011) muffle furnace at C for 4 6 h, then digested with nitric acid (HNO 3 ), washed with distilled water, dried and mounted in Canada balsam. Mazumdar and Mukhopadhyay (2009a,b, 2010) used modified wet oxidation method of Piperno (2006) in which plant materials were digested with concentrated HNO 3 (instead of potassium chlorate +HNO 3 ) in water bath, boiled with 10% hydrochloric acid (HCl) to remove calcium, washed with distilled water, dried with acetone and mounted in 10% glycerine. Sundue (2009) used wet oxidation method of Piperno (1988) in which materials were digested with sulfuric acid (H 2 SO 4 ) and chromic trioxide or hydrogen peroxide (H 2 O 2 ). He also visualized epidermal phytoliths of leaf lamina at 60 magnification in dissection microscope. Kao et al. (2008) found partial polarization light microscopy technique and cryo-tabletop-scanning electron microscopy technique useful for direct visualization of Spicular cells or venuloid idioblasts (long and silica containing epidermal cells) in lamina of Pteris grevilleana. For confirming chemical nature of silica bodies they successfully utilized silica specific dyes Silver-ammine chromate, Crystal Violet Lactone and Methyl Red (developed by Dayanandan et al., 1983) and energy dispersive X-ray spectrometer. 3. Biological significance of phytoliths The occurrence of silicon (Si) within the plant is a result of its uptake, in the form of soluble Si(OH) 4 or Si(OH) 3 O 2, from the soil and its controlled polymerization at a final location (Currie and Perry, 2007). The occurrence of silicon as silica bodies or phytolith in many plants has been correlated with mechanical support (Kaufman et al., 1973), reduction of water loss (Gao et al., 2004), protection from herbivores (Vicari and Bazely, 1993), prevention of entry of pathogens (Nanda and Gangopadhyay, 1984), protection from metal toxicity (Hodson and Evans, 1995), root elongation (Hattori et al., 2003), increased capture of light for photosynthesis (Yoshida et al., 1959), and in cooling of leaves (Wang et al., 2005). Recent findings indicate that silicon protects the plants from various biotic and abiotic stresses by enhancing the production of enzymes and various compounds (like, chitinases, peroxidases, polyphenol oxidases, flavonoid phytoalexins, etc) related to stress resistance, but the detailed mechanism has yet to be fully elucidated (cf. Currie and Perry, 2007). Chen and Lewin (1969) found that silicon is an essential element for the healthy growth of E. arvense and silicon deficient plants showed symptoms like necrosis of the branch tips, wilting or drooping of the branches. In vitro study with E. hyemale by Hoffman and Hillson (1979) indicated that silicon is a required nutrient for spore viability and essential for completion of the life cycle of this plant. Developmental studies also indicated the importance of silicification in mechanical strengthening (Kaufman et al., 1973) and in negative geotropism (Srinivasan et al., 1979)inE. hyemale var. affine. However, evolutionary advantages offered by silicon deposited as silica are still not clearly understood. Chauhan et al. (2009) observed silica deposition of biological origin in different parts of 14 species of pteridophytes (Lycopodium japonicum, Selaginella bryopteris, Actiniopteris australis, Adiantum caudatum, A. phillippense, A. peruvianum, A. venustum, Cyathea gigentea, Doryopteris sagittifolia, Drynaria quercifolia, Gleichenia microphylla, Hemionitis arifolia, Lygodium flexuosum and Pteris vittata) and proposed that the presence of silica in the early land plants suggests that the mechanism of silica absorption and accumulation was developed early in the evolution of terrestrial vegetation, because silica was important for the survival of terrestrial life as it gave mechanical stability of tissues, protection against fungi and pests, and resistance against drought by checking evaporation. In general, however, Silicon concentration in shoots is shown to have declined among land plants in the sequence liverwortsnhorsetails Nclubmosses Nmosses Nangiosperms Ngymnosperms N ferns, and relative shoot Silicon concentrations were, in general, low in angiosperms, gymnosperms and ferns (Hodson et al., 2005). 4. Experimental works on silica with pteridophytes Experimental works with some pteridophytes can provide important insight into the mechanisms by which plants accumulate and deposit silica in various organs. Soluble silica, the raw material for phytolith production, is absorbed as monosilicic or orthosilicic acid [Si(OH) 4 ] from the soil through roots. Different plant species show different modes of silica uptake, notably active, passive or rejective, through low affinity transporter, etc (cf. Currie and Perry, 2007). Fu et al. (2002) documented a novel mechanism of obtaining nutrients and accelerating the weathering of soil minerals in fern Matteuccia. This fern may physically incorporate silicate mineral particles into the root cortex, dissolve inorganic nutrients from the silicate minerals to leave silica particles in the cortex nearly in pure form. Further investigation is required for proper understanding about the silica uptake process in other pteridophytes. Equisetum accumulate high amounts of silica in their plant body and have been used as a model system for understanding silica deposition (bio-silicification) and the ultra-structure of silicified layers in plants. Various techniques such as Electron microprobe analysis by Kaufman et al. (1971), scanning and transmission electron microscopy by Perry and Fraser (1991) and Holzhüter et al. (2003), microtomography, energy dispersive X-ray elemental mapping, small-angle and wide-angle scattering of X-rays by Sapei et al. (2007) and Raman microscopy by Sapei et al. (2007) and Gierlinger et al. (2008) have been used to elucidate ultra-structure details of silicified layers. Kaufman et al. (1971) observed that Silica was deposited primarily in discrete knobs and rosettes on the epidermal surface in E. arvense, but essentially in a uniform pattern on and in the entire outer epidermal cell walls of E. hyemale var. affine. In E. arvense the surface micromorphology was found to be very complex and principally fibrillar, globular and sheet-like ultra-structural motifs of silica were found by Perry and Fraser (1991). Silica was present as a thin layer on the outer surface

4 J. Mazumdar / South African Journal of Botany 77 (2011) Table 1 List of pteridophytes studied for phytoliths. Family Species Studied plant parts Occurrence Status References Lycopodiaceae Lycopodium clavatum L. Whole plant + M Chauhan et al. (2009), Mazumdar and Mukhopadhyay (2009b) " L. japonicum Thunb. Aerial branch + N Mazumdar and Mukhopadhyay (2009b) " Palhinhaea cernua (L.) Franco and Vasc. Aerial + M Mazumdar and Mukhopadhyay (2009b), Author branch (unpublished) " Huperzia selago (L.) Bernh. ex Schrank and Aerial + D Mazumdar and Mukhopadhyay (2009b) Mart. branch Selaginellaceae Selaginella bryopteris (L.) Bak. Whole plant + D Chauhan et al. (2009), Mazumdar and Mukhopadhyay (2009b), Author (unpublished) " Selaginella inaequalifolia (Hook. and Grev.) Aerial shoot + M Mazumdar and Mukhopadhyay (2009b), Spring " Selaginella involvens (Sw.) Spring Aerial shoot + N Mazumdar and Mukhopadhyay (2009b) " Selaginella monospora Spring Aerial shoot + N Mazumdar and Mukhopadhyay (2009b) " Selaginella pentagona Spring Aerial shoot + M Mazumdar and Mukhopadhyay (2009b) " Selaginella plana (Desv. ex Poir.) Hieron. Aerial shoot + N Mazumdar and Mukhopadhyay (2009b) " Selaginella tenera (Hook. and Grev.) Spring Aerial shoot + M Mazumdar and Mukhopadhyay (2009b) " Selaginella chrysocaulos (Hook. and Grev.) Aerial shoot + N Mazumdar and Mukhopadhyay (2009b) Spring " Selaginella velutina A.R. Smith Leaf + D cf. Piperno (2006) Isoetaceae Isöetes coromandelina L. Leaf + M Mazumdar and Mukhopadhyay (2009b) " Isöetes weberi Herter Leaf + D Iriarte and Paz (2009) Ophioglossaceae Botrychium virginianum (L.) Sw. Leaf, spike + M Mazumdar and Mukhopadhyay (2010) " Helminthostachys zeylanica (L.) Hook. Leaf + M Mazumdar and Mukhopadhyay (2010) " Ophioglossum reticulatum L. Leaf + D Mazumdar and Mukhopadhyay (2010), Author (unpublished) Psilotaceae Not studied Equisetaceae Equisetum diffusum D. Don Leaf, stem + D cf. Piperno (2006), Mazumdar and Mukhopadhyay (2010) Marattiaceae Angiopteris evecta (Forst.) Hoffm. Leaf + M Mazumdar and Mukhopadhyay (2010) Osmundaceae Not studied Hymenophyllaceae *Hymenophyllum sp. Leaf cf. Piperno (2006) *Trichomanes sp. Leaf + D cf. Piperno (2006) Gleicheniaceae Dicranopteris linearis (Burm. f.) Und. Leaf + M Mazumdar and Mukhopadhyay (2010) Gleichenia gigantea Wall. ex Hook. Leaf + M Mazumdar and Mukhopadhyay (2010) Gleichenia microphylla R. Br. Whole plant + M Chauhan et al. (2009) Dipteridaceae Not studied Matoniaceae Not studied Lygodiaceae Lygodium flexuosum (L.) Sw. Whole plant + M Chauhan et al. (2009) Anemiaceae Not studied Schizaeaceae Not studied Marsileaceae Marsilea ancylopoda A. Braun Leaf + N Iriarte and Paz (2009) " Marsilea minuta L. Leaf + M Author (unpublished) Salviniaceae Azolla pinnata R. Br. Whole plant + M Author (unpublished) " Salvinia molesta Mitch. Leaf + N Author (unpublished) Thyrsopteridaceae Not studied Loxomataceae Not studied Culcitaceae Not studied Plagiogyriaceae Not studied Cibotiaceae Not studied Cyatheaceae Cyathea gigentea (Wall. ex Hook.) Holtt. Whole plant + N Chauhan et al. (2009) " Cyathea spinulosa Wall. ex Hook. Leaf + M Mazumdar and Mukhopadhyay (2010) Dicksoniaceae Not studied Metaxyaceae Not studied Lindsaeaceae Lindsaea odorata Roxb. Leaf + M Mazumdar and Mukhopadhyay (2010) " Sphenomeris chinensis (L.) Maxon Leaf + M Mazumdar and Mukhopadhyay (2010) Saccolomataceae Not studied Dennstaedtiaceae Hypolepis punctata (Thunb.) Mett. ex Kuhn Leaf + M Mazumdar and Mukhopadhyay (2010) Pteridaceae Acrostichum danaeifolium Langsd. and Fisch Leaf Sundue (2009) " Actiniopteris australis Link Whole plant + D Chauhan et al. (2009), Sundue (2009) " Adiantopsis radiata (L.) Fée Leaf Sundue (2009) " Adiantum abscissum Schrad. Leaf + D Sundue (2009) " Adiantum adiantoides (J. Sm.) C. Chr. Leaf + D Sundue (2009) (continued on next page)

5 14 J. Mazumdar / South African Journal of Botany 77 (2011) Table 1 (continued) Family Species Studied plant parts Occurrence Status References " Adiantum andicola Liebm. Leaf + D Sundue (2009) " Adiantum argutum Splitg. Leaf + D Sundue (2009) " Adiantum cajennense Willd. Leaf + D Sundue (2009) " Adiantum capillus-junonis Rupr. Leaf + D Sundue (2009) " Adiantum capillus-veneris L. Leaf + D Sundue (2009) " Adiantum caryotideum H. Christ Leaf + D Sundue (2009) " Adiantum caudatum L. Whole plant + D Chauhan et al. (2009), Sundue (2009) " Adiantum concinnum Humb. and Bonpl. ex Leaf + D Sundue (2009) Willd. " Adiantum cordatum Maxon Leaf + D Sundue (2009) Adiantum delicatulum Mart. Leaf + D Sundue (2009) Adiantum delicatulum Hook Leaf Sundue (2009) " Adiantum dolosum Kunze Leaf + D Sundue (2009) " Adiantum formosum R. Br. Leaf + D Sundue (2009) " Adiantum fructuosum Poepp. ex Spreng. Leaf + D Sundue (2009) " Adiantum glaucescens Klotzsch Leaf + D Sundue (2009) " Adiantum hispidulum Sw. Leaf + D Sundue (2009) " Adiantum humile Kunze Leaf + D Sundue (2009) " Adiantum incertum Lindman Leaf + D Sundue (2009) " Adiantum intermedium Sw. Leaf + D Sundue (2009) " Adiantum jordanii C.H. Mull Leaf Sundue (2009) " Adiantum kaulfusii Kunze Leaf + D Sundue (2009) " Adiantum kendalii Jenman Leaf + D Sundue (2009) " Adiantum krameri B. Zimmer Leaf + D Sundue (2009) " Adiantum latifolium Lam. Leaf + D Sundue (2009) " Adiantum leprieurii Hook. Leaf + D Sundue (2009) " Adiantum lucidum (Cav.) Spreng. Leaf + D Sundue (2009) " Adiantum lunulatum Burm.f. Leaf + D Sundue (2009) " Adiantum macrophyllum Sw. Leaf + D Sundue (2009) " Adiantum malesianum J. Ghatak Leaf + D Sundue (2009) " Adiantum mcvaughii Mickel and Beitel Leaf + D Sundue (2009) " Adiantum multisorum Sampaio Leaf + D Sundue (2009) " Adiantum oaxacanum Mickel and Beitel Leaf + D Sundue (2009) " Adiantum obliquum Desv. Leaf + D Sundue (2009) " Adiantum paraense Hieron. Leaf + D Sundue (2009) " Adiantum patens Willd. Leaf + D Sundue (2009) " Adiantum peruvianum Klotzsch Whole plant + D Chauhan et al. (2009), Sundue (2009) " Adiantum petiolatum Desv. Leaf + D Sundue (2009) " Adiantum phillippense L. Whole plant + D Chauhan et al. (2009), Sundue (2009) " Adiantum phyllitidis J. Sm. Leaf + D Sundue (2009) " Adiantum platyphyllum Sw. Leaf + D Sundue (2009) " Adiantum poeppigianum (Kuhn) Hieron. Leaf + D Sundue (2009) " Adiantum poiretii Wikstr. Leaf Sundue (2009) " Adiantum polyphyllum Willd. Leaf + D Sundue (2009) " Adiantum pulverulentum L. Leaf + D Sundue (2009) " Adiantum pyramidale (L.) Willd. Leaf + D Sundue (2009) " Adiantum raddianum C. Presl Leaf + D Sundue (2009) " Adiantum reniforme L. Leaf Sundue (2009) " Adiantum scalare R.M. Tryon Leaf + D Sundue (2009) " Adiantum seemanii Hook. Leaf + D Sundue (2009) " Adiantum serratodentatum Willd. Leaf + D Sundue (2009) " Adiantum tenerum Sw. Leaf + D Sundue (2009) " Adiantum terminatum Kunze ex Miq. Leaf + D Sundue (2009) " Adiantum tetraphyllum Humb. and Bonpl. ex Leaf + D Sundue (2009) Willd. " Adiantum tomentosum Klotzsch Leaf + D Sundue (2009) " Adiantum trapeziforme L. Leaf + D Sundue (2009) " Adiantum trichochlaenum Mickel and Beitel Leaf + D Sundue (2009) " Adiantum tricholepis Fée Leaf + D Sundue (2009) " Adiantum venustum D. Don Whole plant + D Chauhan et al. (2009), Sundue (2009) " Adiantum villosissimum Kuhn Leaf + D Sundue (2009) " Adiantum villosum L. Leaf + D Sundue (2009) " Adiantum vogellii Mett. ex Keys Leaf + D Sundue (2009) " Adiantum wilsonii Hook. Leaf + D Sundue (2009)

6 J. Mazumdar / South African Journal of Botany 77 (2011) Table 1 (continued) Family Species Studied plant parts Occurrence Status References " Afropteris repens Alston Leaf + D Sundue (2009) " Aleuritopteris argentea (S.G.Gmel.) Fée Leaf Sundue (2009) " Aleuritopteris aurantiacea (Cav.) Ching Leaf Sundue (2009) " Aleuritopteris farinosa (Forssk.) Fée Leaf Sundue (2009) " Ananthacorus angustifolius (Sw.) Underw. and Leaf + D Sundue (2009) Maxon " Anetium citrifolium (L.) Splitg. Leaf + D Sundue (2009) " Anogramma leptophylla (L.) Link Leaf Sundue (2009) " Anopteris hexagona (L.) C. Chr. Leaf Sundue (2009) " Antrophyum boryanum (Willd.) Spreng. Leaf + D Sundue (2009) " Antrophyum callifolium Blume Leaf + D Sundue (2009) " Antrophyum latifolium Bl. Leaf + D Sundue (2009) " Antrophyum lineatum (Sw.) Kaulf. Leaf + D Sundue (2009) " Antrophyum mannianum Hook. Leaf + D Sundue (2009) " Antrophyum minersum Bory Leaf + D Sundue (2009) " Antrophyum plantagineum Cav. Leaf + D Sundue (2009) " Antrophyum reticulatum (Forst.) Kaulf. Leaf + D Sundue (2009), Mazumdar and Mukhopadhyay (2010) " Antryophum brasilianum (Desv.) C. Chr. Leaf + D Sundue (2009) " Antryophym obovatum Baker Leaf + D Sundue (2009) " Argyrochosma limitanea (Maxon) Windham Leaf Sundue (2009) " Aspidotis californica (Hook.) Nutt. ex Copel. Leaf + N Sundue (2009) " Aspidotis densa (Brack) Lellinger Leaf + N Sundue (2009) " Astrolepis sinuata (Lag. ex Sw.) D.M. Benham Leaf Sundue (2009) and Windham " Austrogramme decipiens (Mett.) Hennipman Leaf Sundue (2009) " Bommeria hispida (Mett. ex Kuhn) Underw. Leaf Sundue (2009) " Ceratopteris pteridoides (Hook.) Hieron. Leaf Sundue (2009) " Ceratopteris richardii Brongn. Leaf Sundue (2009) " Cheilanthes alabamensis (Buckley) Kunze Leaf Sundue (2009) " Cheilanthes albomarginata Clarke Leaf + N Sundue (2009), Mazumdar and Mukhopadhyay (2010) " Cheilanthes angustifolia Kunth Leaf Sundue (2009) " Cheilanthes cuneata Kaulf. ex Link Leaf Sundue (2009) " Cheilanthes decomposita (M. Martens and Leaf Sundue (2009) Galeotti) Fée " Cheilanthes eatonii Baker Leaf Sundue (2009) " Cryptogramma cripsa (L.) R. Br. ex Hook. Leaf Sundue (2009) " Doryopteris ludens (Wall ex Hook.) J. Sm. Leaf Sundue (2009) " Doryopteris sagittifolia J. Sm. Whole plant + N Chauhan et al. (2009), Sundue (2009) " Eriosorus hispidulus (Kunze) Vareschi Leaf Sundue (2009) " Haplopteris anguste-elongata Hay Leaf + D Sundue (2009) " Haplopteris elongata (Sw.) E.H. Crane Leaf + D Sundue (2009) " Haplopteris ensiformis Sw. Leaf + D Sundue (2009) " Haplopteris flexuosa Fée Leaf + D Sundue (2009) " Haplopteris forestiana Ching Leaf + D Sundue (2009) " Haplopteris zosterifolia Willd. Leaf + D Sundue (2009) " Hecistopteris pumila (Spreng.) J. Sm. Leaf + D Sundue (2009) " Hemionitis arifolia (Burm.) Moore. Whole plant + N Chauhan et al. (2009), Sundue (2009) " Hemionitis rufa (L.) Sw. Leaf Sundue (2009) " Jamesonia verticalis Kunze Leaf Sundue (2009) " Llavea cordifolia Lag. Leaf Sundue (2009) " Mildella intramarginalis (Kaulf. ex Link) Leaf + D Sundue (2009) Trevis. " Monogramma graminea (Poir.) Leaf + D Sundue (2009) " Monogramma paradoxa (Fée) Leaf + D Sundue (2009) " Neurocalis praestantissima Bory ex Fée Leaf Sundue (2009) " Onychium japonicum Blume Leaf + D Sundue (2009) " Onychium siliculosum (Desv.) C. Chr. Leaf + D Sundue (2009) " Pentagramma triangularis (Kaulf.) Yatsk., Leaf Sundue (2009) Windham and E.Wollenw. " Pityrogramma austroamericana Domin Leaf + D Sundue (2009) " Pityrogramma calomelanos (L.) Link Leaf + D Sundue (2009) " Pityrogramma ebenea (L.) Proctor Leaf + D Sundue (2009) " Pityrogramma trifoliata (L.) R.M. Tryon Leaf + D Sundue (2009) (continued on next page)

7 16 J. Mazumdar / South African Journal of Botany 77 (2011) Table 1 (continued) Family Species Studied plant parts Occurrence Status References " Platyzoma microphyllum R. Br. Leaf Sundue (2009) " Polytaenium cajenense (Desv.) Spreng. Leaf + D Sundue (2009) " Polytaenium chlorosporum (Mickel and Beitel) Leaf + D Sundue (2009) E.H.Crane " Polytaenium guayanense (Hieron.) Alston Leaf + D Sundue (2009) " Polytaenium lanceolatum (L.) Desv. Leaf + D Sundue (2009) " Polytaenium lineatum (Sw.) J. Sm. Leaf Sundue (2009) " Polytaenium urbanii (Brause) Alain Leaf + D Sundue (2009) " Pteris arborea L. Leaf Sundue (2009) " Pteris argyraea T. Moore Leaf Sundue (2009) " Pteris mulitifida Poir. Leaf + D Sundue (2009) " Pteris propinqua J. Agardh Leaf Sundue (2009) " Pteris quadriaurita Retz. Leaf Sundue (2009) " Pteris ryukyuensis Tagawa Leaf + D Sundue (2009) " Pteris tremula R. Br. Leaf Sundue (2009) " Pteris vittata L. Whole plant + D Chauhan et al. (2009), Sundue (2009) " Pterozonium brevifrons (A.C. Sm.) Lellinger Leaf + D Sundue (2009) " Radiovittaria gardneriana (Fée) E.H. Crane Leaf + D Sundue (2009) " Radiovittaria minima (Benedict) E.H. Crane Leaf + D Sundue (2009) " Radiovittaria remota (Fée) E.H. Crane Leaf + D Sundue (2009) " Scoliosorus ensiformis (Hook.) T. Moore Leaf + D Sundue (2009) " Vittaria amboinensis Fee Leaf + D Mazumdar and Mukhopadhyay (2010) " Vittaria carcina Christ. Leaf + D Mazumdar and Mukhopadhyay (2010) " Vittaria elongata Sw. Leaf + D Mazumdar and Mukhopadhyay (2010) " Vittaria flavicosta Mickel and Bietel Leaf + D Sundue (2009) " Vittaria graminifolia Kaulf. Leaf + D Sundue (2009) " Vittaria himalayensis Ching Leaf + D Mazumdar and Mukhopadhyay (2010) " Vittaria isoetifolia Bory Leaf + D Sundue (2009) " Vittaria lineata (L.) J.E. Sm. Leaf + D Sundue (2009) " Vittaria sikkimensis Kuhn Leaf + D Mazumdar and Mukhopadhyay (2010b) " Vittaria zosterifolia Willd. Leaf + D Mazumdar and Mukhopadhyay (2010) Aspleniaceae Not studied Woodsiaceae Athyrium nigripes (Bl.) Moore Leaf + M Mazumdar and Mukhopadhyay (2010) " Diplazium esculentum (Retz.) Sw. Leaf + M Mazumdar and Mukhopadhyay (2010) Thelypteridaceae Ampelopteris prolifera (Retz.) Copel. Leaf + M Mazumdar and Mukhopadhyay (2010) " Christella dentata (Forssk.) Brownsey and Leaf + M Mazumdar and Mukhopadhyay (2010) Jermy " Cyclosorus interruptus (Willd.) H. Itô Leaf + M Mazumdar and Mukhopadhyay (2010) " Pronephrium nudatum (Roxb. ex Griff.) Holtt. Leaf + M Mazumdar and Mukhopadhyay (2010) " Pseudocyclosorus tylodes (Kunze) Ching Leaf + M Mazumdar and Mukhopadhyay (2010) " Pseudophegopteris pyrrhorhachis var. glabrata (Clarke) Holtt. Leaf + M Mazumdar and Mukhopadhyay (2010) Blechnaceae Blechnum orientale L. Leaf + D Mazumdar and Mukhopadhyay (2010), Author (unpublished) Onocleaceae Not studied Dryopteridaceae Leucostegia immersa (Wall. ex Hook.) Presl Leaf + M Mazumdar and Mukhopadhyay (2010) Peranema cyatheoides D. Don Leaf + M Mazumdar and Mukhopadhyay (2010) Polystichum squarrosum (D. Don) Fee Leaf + M Mazumdar and Mukhopadhyay (2010) Lomariopsidaceae Not studied Tectariaceae Not studied Oleandraceae Oleandra wallichi (Hook.) Pr. Leaf + M Mazumdar and Mukhopadhyay (2010) Davalliaceae Not studied *Polypodiaceae Arthromeris wallichiana (Spreng.) Ching Leaf + M Mazumdar and Mukhopadhyay (2010) Drynaria quercifolia (L.) J. Sm. Whole plant + M Chauhan et al. (2009) Phymatopteris griffithiana Pic. Ser. Leaf + M Mazumdar and Mukhopadhyay (2010) Systematic positions of families and species of ferns were adapted from Smith et al. (2006). Abbreviations: + = phytoliths present, = phytoliths absent, D = phytoliths diagnostic, M = phytoliths might be diagnostic but require further study, N = phytoliths not diagnostic, * = name of the species not mentioned in available literature. with dense arrangement of silica spheres, and a loose arrangement of silica particles was found beneath this, suggesting the agglomeration of silica (Holzhüter et al., 2003). Some studies provided insight into the mechanism of biosilicification and its regulation. Hydrated amorphous silica is a colloidal mineral that aggregate (polycondensates) into various

8 J. Mazumdar / South African Journal of Botany 77 (2011) Table 2 Features of diagnostic phytoliths. Taxa Features Plant parts Diagnostic at References Huperzia selago (L.) Bernh. ex Schrank and Mart. (Lycopodiaceae) Smooth or granular plates with projecting margins (Fig. 1A) Aerial branch Species level Mazumdar and Mukhopadhyay (2009b), Author (unpublished) Selaginellaceae Elongated epidermal bodies with small cone like projections (Fig. 1E) Leaf Family level cf. Piperno (2006), Chauhan et al. (2009), Mazumdar and Mukhopadhyay (2009b) Isöetes weberi Herter (Isoetaceae) Epidermal cells like angular, Leaf Species level Iriarte and Paz (2009) polyhedral bodies Ophioglossum reticulatum L. (Ophioglossaceae) Epidermal plates with smooth surface and sinuate margins Leaf Species level Mazumdar and Mukhopadhyay (2010), Author (unpublished) Equisetaceae Smooth or granular epidermal plates with elevated projections along the edges (Fig. 1D) Nearly rectangular granular epidermal plates with dentate margins (Fig. 1D) Leaf, stem Family level cf. Piperno (2006), Mazumdar and Mukhopadhyay (2010) Equisetum diffusum D. Don (Equisetaceae) Leaf, stem Species level Mazumdar and Mukhopadhyay (2010) Hymenophyllaceae Roughly bowl-shaped Leaf Family level cf. Piperno (2006) Adiantoid clade (Pteridaceae) Elliptical shape, tapered ends and Leaf Clade level Sundue (2009), Chauhan et al. (2009), undulate sides (Fig. 1C) Mazumdar and Mukhopadhyay (2010) Pteridoid clade (Pteridaceae) Blunt ends and sides that are smooth, Leaf Clade level Sundue (2009), Chauhan et al. (2009) denticulate sparsely denticulate or shallowly lobed Blechnum orientale L. (Blechnaceae) Polypodiaceae Elongated epidermal plates with smooth surface and lobed margins (Fig. 1B) Elongated flat base and a surface with two undulating ridges parallel to each other Leaf Species level Mazumdar and Mukhopadhyay (2010), Author (unpublished) Leaf Family level cf. Piperno (2006) microscopic and macroscopic forms. Protein containing biosilica extracts from E. telmateia was found to influence the kinetics of silica formation and structure (Perry and Keeling-Tucker, 2003). The close association of silica with cell wall polymers suggests that they may act as a polymeric template that controls the shape and size of the colloidal silica particles (Sapei et al., 2007). Gierlinger et al. (2008) suggested the roles of pectin and hemicelluloses in silica deposition in E. hyemale. Currie and Perry (2009) found the association of silicon with soluble carbohydrate and proteinaceous components in cell walls of E. arvense and suggested the possible role of silicon in cross-linking the cell wall polymers, thereby providing a modest improvement in rigidity or stability of the cell wall against biotic and abiotic stresses. 5. Conclusion Phytoliths of pteridophytes can provide important insights into past vegetations (Piperno, 2006). Table 1 showed that 225 pteridophytic species have been studied and phytoliths were detected in 168 species. In 168 species studied, phytoliths were diagnostic in 121 species, might be diagnostic in 34 species and not diagnostic in 13 species. So, Table 1 indicated that phytoliths in pteridophytes have immense probability to be useful as taxonomic tools in future for delineation of family (e.g., Polypodiaceae), genus (e.g., Equisetum) and species (e.g., Isöetes weberi) (other examples in Table 2) and also for phylogenetic analysis (e.g., Pteridaceae). As shown in Table 1 only Pteridaceae is the more studied family than others. No investigations were conducted in 19 families (Psilotaceae, Osmundaceae, Dipteridaceae, Matoniaceae, Anemiaceae, Schizaeaceae, Thyrsopteridaceae, Loxomataceae, Culcitaceae, Plagiogyriaceae, Cibotiaceae, Dicksoniaceae, Metaxyaceae, Saccolomataceae, Aspleniaceae, Onocleaceae, Lomariopsidaceae, Tectariaceae, and Davalliaceae) and less sampling was made in 20 families (Lycopodiaceae, Selaginellaceae, Isoetaceae, Ophioglossaceae, Equisetaceae, Marattiaceae, Hymenophyllaceae, Gleicheniaceae, Lygodiaceae, Marsileaceae, Salviniaceae, Cyatheaceae, Lindsaeaceae, Dennstaedtiaceae, Woodsiaceae, Thelypteridaceae, Blechnaceae, Dryopteridaceae, Oleandraceae, and Polypodiaceae). Also, leaves were extensively studied (in 181 species) than other parts like aerial branches (in 11 species), rhizomes (in 11 species) and roots or whole plants (in 15 species). Epidermal phytoliths were found to be more useful as diagnostic characters in all investigations. However, Chauhan et al. (2009) noted silicified hairs in Cyathea gigentea, silicified hair bases in Lygodium flexuosum, silicified tracheids in Actiniopteris australis, etc. But, taxonomic utility of these phytoliths require further investigations. Phytoliths are also important for normal growth and survival of pteridophytes as exemplified by works on some species of Equisetum. Experimental works with pteridophytes will elucidate the mechanism by which plants uptake silica from soil, deposit in distinct layers and regulate the formation of silica micro and macro structures. It might be helpful in generation of new materials with specific form and function for industrial application (Perry and Keeling-Tucker, 2003) and also in nanotechnology (Neethirajan et al., 2009). Acknowledgements I express my sincere thanks to Dr. J. Manning, Review Board Editor, South African Journal of Botany and reviewers for

9 18 J. Mazumdar / South African Journal of Botany 77 (2011) reviewing and improving the quality of manuscript. I am grateful to Prof. R. Mukhopadhyay, Department of Botany, The University of Burdwan, India for giving valuable suggestions. I thank Dr. M. Sundue, The New York Botanical Garden, New York, USA; Dr. J. Iriarte, Department of Archaeology, University of Exeter, UK and Dr. M.W. Chase, Jodrell Laboratory, Royal Botanic Gardens, Kew, UK for kindly providing reprints. References Chase, M.W., Reveal, J.L., A phylogenetic classification of the land plants to accompany APG III. Botanical Journal of the Linnean Society 161, Chauhan, D.K., Tripathi, D.K., Sinha, P., Tiwari, S.P., Biogenic silica in some pteridophytes. Bionature 29, 1 9. Chen, C.-H., Lewin, J., Silicon as a nutrient element for Equisetum arvense. Canadian Journal of Botany 47, Currie, H.A., Perry, C.C., Silica in plants: biological, biochemical and chemical studies. 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10 J. Mazumdar / South African Journal of Botany 77 (2011) Tubb, H.J., Hodson, M.J., Hodson, G.C., The inflorescence Papillae of the Triticeae: a new tool for taxonomic and archaeological research. Annals of Botany 72, Vicari, M., Bazely, D.R., Do grasses fight back? The case for antiherbivore defences. Trends in Ecology & Evolution 8, Wang, L., Nie, Q., Li, M., Zhang, F., Zhuang, J., Yang, W., Li, T., Wang, Y., Biosilicified structures for cooling plant leaves: a mechanism of highly efficient midinfrared thermal emission. Applied Physics Letters 87, Yoshida, S., Onshi, Y., Kitagishi, K., The chemical nature of silicon in rice plant. Soil Plant Food (Tokyo) 5, Edited by JC Manning