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Vascular Morphology of Stipe and Rachis in Some Western Himalayan

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Vascular Morphology of Stipe and Rachis in Some Western Himalayan Proc. Indian Acad. Sci. (Plant Sci.), Vol. 100, No. 6, December 1990, pp. 399-407. 9 Printed in India. Vascular morphology of stipe and raehis in some western Himalayan species of Pteris Linn. N PUNETHA Department of Botany, Government PG College, Pithoragarh 262 501, India MS received 25 June 1990; revised 10 December 1990 Abstraet. Vascularsupply to leaf in 8 species of the fern genus Pteris is described. Except in Pteris cretica in which the stipe is supplied by a pair of ribbon like vascular bundles, stipe vasculature of the other 7 species studied is solitary and gutter-shaped; in transection the vascular bundle in Pteris cretica, Pteris dactylina and Pterts stenophylla is V-shaped, ~- shaped in Pteris wallichiana and horse-shoe shaped in others. In Pteris vittata and Pteris wallichiana pinna trace is extra marginal in origin while in all others it is marginal. Based on number and structure of vascular strand and nature of origin of pinna traces it is concluded that Pteris crelica and Pteris oittata are relatively advanced over other species with simply pinnate fronds. Pteris wallichiana has been considered as highly evolved among the species investigated. Keywords. Adaxial xylem plate; leaf vasculature; fl-shaped vascular bundle; pinna trace; Pteris. 1. Introduction Leaf vasculature in ferns is to a larger extent related with the morphotogy of the frond and it has also been considered as of significance in fern taxonomy (Ogura 1972; Lin and De Vol 1977). In addition to main vascular supply to frond, the primary pinna traces are also of taxonomic significance (Bower 1926). Apart from (being helpful in fern) taxonomy, the leaf vasculature can be useful in tracing phylogenetic relationships within various groups (Bower 1926). While describing the rhizome morphology of Pteris indica var. integrifolia Bedd. and Pteris wallichiana Ag. Tansley and Lulham (1904) and Mehra (1944) also made mention of the structure of leal trace in these ferns respectively. Although some aspects of vascular structure of stipe of some Indian species of Pteris have been discussed by Chandra and Nayar (1970) and Khare and Shankar (1989), available literature on stipe anatomy of ferns (Tansley and Lulham 1904; Tansley 1907, 1908; Sinnot 1911; Davie 1918) reveal that there is no detail information on the leaf vasculature of the polymorphic genus Pteris. In view of this the leaf vasculature in 8 species of Pteris was studied. 2. Materials and methods Fresh materials of all the 8 species (table 1) of Pteris collected from different localities of Pithoragarh district of Kumaon (western Himalaya) was fixed in FAA (1 : 1 : 3) for 48 h and then stored in 70% ethyl alcohol. Anatomy of stipe and rachis was studied from microtome and/or hand sections stained with safranin and fastgreen. Stelar reconstructions are based on serial sections cut at 8-10#m. Special attention was paid to the general form and shape of the vasculature and 399 4~ g: Table I. Characteristics of leaf vasculature in 8 species of Pteris. P. cretica P. dactylina P. stenophylla P. vittata P. excelsa P. quadriaurita P. biaurita P. wallichiana No. of xylem strand 2 I I I 1 1 I 1 Size of xyelm strand ix0.75 ~~xO-70 lxO.80 3.8x2.8 3.5x3.5 2.2x2.0 2.5x2-3 6.5x6.0 at stipe base (mm)* Shape of leaf vascu- V V V U U U U li lature in TS No. of protoxylem groups At stipe base 2 in each str- 3 3 14-16 20-24 13-16 12-13 44-50 and At stipr apex 4 3 3 4-6 6-8 10-12 7-8 39--40 Formation ofadaxial No No No No No No No Yes xylem plate Nature of pinna trace Marginal Marginal Marginal Extra-marginal Marginal Marginal Marginal Extra-marginal Shape of pinna trace Flat Fiar Flat U U U U *Averages of 6 samples. Vascular morphology of stipe and rachis in Pteris 401 nature of pinnae traces. Voucher specimens are deposited in the Pteridology laboratory, Department of Botany, Government PG College, Pithoragarh, India. 3. Resuits The leaves arise in spiral succession on the creeping or erect rhizome. Except P. cretica Linn., only one vascular bundle is present in the species investigated (table 1). In P. cretica two ribbon-like vascular bundles are presentat the base of the stipe and both the margins of the xylem strand of each are incurved (figures 2, 21). The abaxial margins of vascular bundles are nearer to each other than the adaxial margins. Protoxylem elements are confined to both margins of each bundle. A little higher up in the stipe a few metaxylem elements are added marginally in the abaxial protoxylem groups of both the bundles which come closer and fuse with each other. The single vascular bundle thus comprises two marginal protoxylem groups in addition to two more in the abaxial arc. The vascular bundle in cross section is V-shaped (figures 4, 22). In specimens with short stipe the two vascular ~p f 'i ~ -t.! r: ~L ~~4 to t S It q~ -, ,fl~ .ti ,~ . Figures 1-14. 1. Reconstruction of leaf vasculature in P. cretica. 2-7. Successive stages of xylem strand in P. cretica Icross sections). 8. Reconstruction of leaf vasculature in P. dactylina. 9--12. Successive stages of xylem strand in P. dactylina. 13. Shape of xylem strand lin cross section) at the stipe base in P. vittata. 14. Reconstruction of leaf vasculature in P. vittata. 15. Reconstruction of leaf vasculature in P. stenophylla. 16. Reconstruction of leaf vasculature in P. biaurita. (blp, Basal lateral pinna; lp, lateral pinna; s, stipe; tp, terminal pinna). 402 N Punetha Figures 17-20. 17. Reconstruction of leaf vasculature in P. wallichiana. 18-20. Successive stages of xylem strand in P. waUichiana (cross sections). bundles unite at the base of the stipe (two distinct vascular bundles arise from the rhizome), in some others the union of bundles took place almost half way up in the stipe, in still others (especially in long stiped fronds) they unite farther up in the stipe but definitely before the departure of the pinna trace. Nearer to stipe apex the adaxial protoxylem elements of each arm increase in number which mark the formation of the pinna trace to basal pinnae. About 1-1.5 cm behind the basal pair of pinnae an abstriction appears next to the free adaxial margins of each arm of the protoxylem group which deepens gradually and from each arre is given off marginally one pinna trace (figures 1, 5) which supplies the basal pinnae on that side. In few specimens the united drain-like main vascular bundle passes upward in the rachis and splits into two strap shaped vascular bundles which, however, reunite before giving off pinnae traces to the second pair of the lateral pinnae (figures 1, 6, 7). In other specimens the main bundle does not split after supplying to basal pair of lateral pinnae and only one bundle is maintained throughout, from which the pinnae traces are given off successively and ultimately a shallow drain-like bundle enters the terminal pinna. Only one vascular bundle supplies each leal in P. dactylina Hook. and P. stenophylla WaU. Three protoxylem groups, one each at the margins of free arras and the third abaxially at the place of union of two arras of V (in cross section of Vascular morphology of stipe and rachis in Pteris 403 9:~ ~. ,-, . ' ~.1,% Figures 21-27. Vascular bundles in cross sections. 21. P. cretica, showing binary leaf trace. 22. P. cretica, fusion of two vascular bundles from their abaxial margins. 23. P. dactylina, V-shaped vascular bundle prior to the departure of the pinna trace. 24. P. stenophylla, V-shaped vascular bundle just before the separation of pinna trace (from the left arm}. 25. P. vittata, vascular bundle showing departing pinna trace extra- marginally (from the left arre). 26-27. Successive stages of o¡ of extra-marginal pinna trace in P. vittata. stipe the vascular bundle is V-shaped) remain unchanged throughout the length of the stipe. The marginal protoxylem groups are incurved and relatively more divergent in P. dactylina (figures 8, 9, I0, 23). Towards the stipe apex the marginal protoxylem elements increase in number and arranged in ah oblique linear row to constitute the pinna trace. Thus, most of the marginal protoxylem elements ate used up in building the pinna trace. The pinna trace which mainly comprises the 404 N Punetha protoxylem elements is detached from the mother strand simply by an abstriction at the posterior part of the marginal protoxylem group (figures 11, 12, 15, 23, 24). Relatively large gutter-shaped vascular bundle is found in P. vittata Linn. (figures 13, 25), P. excelsa Gaud., P. quadriaurita Retz. (figure 28) and P. biaurita Linn. (figure 16). Fairly large number of protoxylem groups alter with metaxylem groups in the xylem arc at the base of the stipe (table 1). This number is gradually reduced towards the stipe apex. The margins of the crescent at the base of stipe comprising metaxylem elements are incurved in P. excelsa, P. quadriaurita and P. biaurita. In P. vittata in addition to two protoxylem groups (separated by metaxylem), two more protoxylem groups are present in the hooked marginal part of the two arms (figure 25). Xylem elements at the extreme margins are larger than the normal protoxylem elements next to them. Up in the stipe, the sub-marginal protoxylem elements extend iaterally, increase in number and ate arranged in a circular ring (figures 25-27). This circular protoxylem group gradually separates from the mother strand and enters in the lateral pinna.
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