On the identity and occurrence of Ophioglossum costatum (Pteridophyta: Ophioglossaceae) in Andhra Pradesh, India

1462 The members of the genus Ophioglossum L. (Ophioglossaceae) are known as snake tongue or adder’s tongue ferns. The genus comprises, worldwide, an estimated 28-58 (Panigrahi & Dixit 1969) to 40 species (Singh et al. 2009). In India, it is represented by 12 species (Yadav & Tripathi 2002; Goswami et al. 2008; Singh et al. 2009). Pullaiah et al. (2003) recorded three species of the genus for the state of Andhra Pradesh, namely, Ophioglossum gramineum Willd., O.nudicaule L.f. and O. reticulatum L. However, earlier Rao et al. (1999) reported O. pedunculosum Desv. to be common on the hills of Tuni in East Godavari District which is synonymous with Ohioglossum costatum R.Br. a distinct, widespread

species often misidentified with O. nudicaule L.f. The present paper attempts to look at this problem and adds a note on the field identity and occurrence of the paleotropical fern, Ophioglossum costatum R.Br., in Andhra Pradesh.

Taxonomic identity
In the herbarium, often, the differences between the specimens of O. costatum and O. nudicaule are not perceived properly and confused when the particulars of the subterranean parts such as rhizome shape, size, number of fibrous roots, origin of trophophylls, depth at which the rhizome is buried, presence of stolons, etc. are missing or not indicated. Table 1 provides the differences between these species for their proper identification.
Although the sterile fronds arise from the subterranean part of the rhizome in O. costatum, O.nudicaule and O. polyphyllum, the plants attain a height of about 4cm, the rhizome is tuberous, cylindrical with a growing point, stolons help in vegetative propagation, the angle between peduncle and lamina is 90 0 and the venation of the sterile frond is not double in O. nudicaule. The plants can reach a height of 25cm, the rhizome is globose, tuberous with an apical cupule, no stolons but bear profuse lateral roots and the trophophyll is with a distinct pale midrib in O. costatum, whereas, the sterile fronds are many (2-5; usually 4) and without the distinct costa in O. polyphyllum. Diagnosis: Perennial herbs (geophyte) of 13-19.7 cm high; rhizome tuberous, globose (Image 1d), 0.6 to 1 cm diam., with 37-54 lateral, fibrous, radiating or descending, non-proliferous roots arising from the entire periphery of the knob-like rhizome except at the bottom (Images 1c,e); stolons absent. Trophophylls (sterile fronds) 2 or 3, rarely 4 (even 5 c.f. Beddome, loc. cit. ff. 72, 289) or single arising from a crater (pitlike depression); 3-7 x 1-3 cm, green with distinct pale midrib; usually flat, at times folded or concave; ovate or ovate-lanceolate or elliptic, slightly fleshy, broadly cuneate at base; apex acute to obtuse; margin entire or wavy; standing at 40-60 0 from the ground; trophophore 70-90% of its length subterranean.   Rhizome (Diameter/length) 0.6-0.9 cm. 0.42 ± 0.02 cm.
(c) Distribution Arising mostly on the circumference of the knob-like rhizome.
Arising on the entire length of the rhizome.
(d) Stolons Absent (no vegetative propagation by stolons). Frequently present, arising from the base of rhizome.

Trophophylls (Sterile fronds):
(a) Origin Arising from the centre of the cupule of the rhizome. Arising from the tip of the rhizome. Note: (i) Plate 2 by Pullaiah et al. (2003) carry the picture of plants of Ophioglossum nudicaule from Chandragiri, Chittoor District which clearly pertain to O. costatum. Prof. R.R.V. Raju (pers. comm.) confirms the herbarium specimen cited above of the collector at SKU as of O. costatum; (ii) Pullaiah et al. (2003) also failed to record the presence of O. pedunculosum in Tuni Hills of East Godavari District of Andhra Pradesh reported by Rao et al. (1999); O. pedunculosum Desv. is now treated conspecific with O. costatum R.Br.; (iii) The specimens of O. costatum from Madhya Pradesh and Chattisgarh were found to be larger bearing long elliptic leaves, etc. (Balakrishnan et al. 1960); (iv) Although O. costatum is not in endangered list, its habitats are threatened due to alien plant invasions (by Hyptis suaveolens, Parthenium hysterophorus, etc.), grazing (Image 1h), etc.