Proc. Indian Acad. Sci. ( Sci.), Vol. 100, No. 6, December 1990, pp. 399-407. 9 Printed in India.

Vascular morphology of stipe and raehis in some western Himalayan of Linn.

N PUNETHA Department of , Government PG College, Pithoragarh 262 501, India MS received 25 June 1990; revised 10 December 1990 Abstraet. Vascularsupply to in 8 species of the 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 plate; leaf vasculature; fl-shaped vascular bundle; pinna trace; Pteris.

1. Introduction

Leaf vasculature in is to a larger extent related with the morphotogy of the frond and it has also been considered as of significance in fern (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 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 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. In the meantime the marginal xylem elements rejoin the main strand. Thus, the pinna trace which mainly comprises the protoxylem elements originates extramarginally without the formation of any gap (figures. 14, 27). New protoxylem elements develop behind the marginal metaxylem group which constitute the next pinna trace. The large gutter-shaped leal vasculature in P. excelsa, P. quadriaurita and P. biaurita generally remain unchanged except that it gradually narrows towards the stipe apex and the number of protoxylem groups are reduced in the process. The marginal protoxylem elements increase in number, extend adaxially somewhat obliquely in a linear row and separate from the mother strand by an abstriction to form the pinna trace. Pinna trace is gutter-shaped. For next pinna trace new protoxylem elements are added marginally. Leaf vasculature in P. wallichiana is entirely different from other species examined in this study. Fairly large gutter-shaped (figure 17) vascular bundle arises from the

Figures 28-29. 28. U-shaped xylem strand in P. quadriaurita (TS of stipe). 29. TS of the base of terminal pinna of P. wallichiana showing re-union of adaxial xylem plate with corresponding circular main strand to supply the terminal pinna. Vascular raorphology of stipe and rachis in Pteris 405

erect rhizome with the open end (in transection the vascular bundle is f2-shaped) facing the adaxial side (figure 18). This configuration is maintained throughout the length of the stipe. At the stipe apex, however, both size and shape of the vascular bundle change remarkably which ate noticeable about 2 cm behind the trifurcation (of the lamina). The vascular bundle becomes compressed along the invagination and the marginal flaps unite with each other, consequently an adaxial xylem plate is separated from the main bundle which now becomes circular (figure 19). From the circular bundle 3 daughter circular bundles ate formed (figure 20). The adaxial xylem plate also splits into 3 almost equal parts by two abstrictions. One daughter adaxial xylem plate anda corresponding daughter circular bundle constitute the vascular bundte for one rachis branch (figures 17, 29). A median slit in the adaxiai xylem plate make the vascular bundle f Pinna trace originates partly from the bulged region of the vascular bundle and partly from the marginal flap of that side. The protoxylem group of the bulged region increase in number, extend laterally and make a circular ring, which soon separates from the mother bundle. At the same time the submarginal protoxylem elements of the corresponding marginal flap also increase in number. An abstriction in this region separates the marginal flap. The circular ¡ and the detached marginal flap together constitute a pinna trace. A median slit in the detached marginal flap make the pinna trace ~-shaped.

4. Discussion

Fronds of P. cretica, P. dactylina, P. stenophylla and P. vittata are 1-pinnate; those of P. excelsa and P, quadriaurita are bipinnate and of P. biaurita is l-pinnate and pinnatifid (commonly termed as bipinnatifid) whereas P. wallichiana is tripartite with each part pinnatifid. In P. biaurita a series of costal areoles and in P. wallichiana, a series of costular areole3 in addition to the costal areoles is also present in each segment whereas the veins in rest of the species examined ate forked. Anastomosing of veins and the presence of more than one leal trace are believed to be advance characters over dichotomous veins and solitary leal trace respectively. Within pinnate forros thus, it seems that P. dactylina and P, stenophylla ate primitive and P. cretica and P. vittata ate relatively advance. In P. vittata the pinnae traces are extramarginal, the character usually considered as advance (Bower 1923). Vascular supply of the frond in P. wallichianna is interesting in that it is f2- shaped and thus more advanced than in the other species studied. The size and shape of the leaf vasculature is associated with the general morphology of the frond. Among the species studied P. wallichiana bears the largest fronds. The nature of vascular supply to the lateral pinnae suggests that the basal lateral pair of pinnae ate morphologically not similar to the lateral pair of pinnae of other species. Union of xylem strands at the invagination (Chandra and Nayar 1970) followed by separation of free arras of 'tq' from the rest of the xylem to forman 'adaxial xylem plate' and formation of a circular xylem strand ate unique features. Further, forrnation of 3 circular xylem strands from the main strand, breaking of the adaxial xylem plate into 3 parts and re-union of the adaxial plate (daughter) with its corresponding circular xylem strand ieave no doubt that morphologically the lateral pinnae are identical to the terminal pinna. Almost identical vascular supply to fronds is known in gleichenioid ferns (Chrysler 1943, 1944; Punetha 1984). 406 N Punetha

Although no structure like adaxial xylem plate is formed in the leaf vasculature of gleichenioid ferns, formation of 3 circular vascular bundles at each fork is much alike. Of the 3 circular vascular bundles, the lateral two enter in the 'lateral rachis branches' whereas the middle one supplies the dormant apex. Before defining precisely the branching of the leaf in gleichenioid ferns Holttum (1954) referred the laminar lateral pinnae as 'the lateral branches' and the terminal pinna as 'the middle branch' in P. tripartita Sw. (a species similar in branching of frond to P. wallichiana). Holttum (1957, 1959) coined the term 'rachis branches' to the lateral structures on the frond axes of gleichenioid ferns. The vascular supplies of the 'rachis branches' are similar to the vascular supply of'main rachis' a situation very much similar to that of P. wallichiana. Further branching of terminal pinna and lateral pinnae is identical in P. wallichiana and P. tripartita. The lateral laminar structures in these species are morphologically and anatomoically identical to the terminal one. It is, therefore, not appropriate to use the term 'lateral pinnae' for these structures and should be termed as 'rachis branches' a term already in use. It appears that the similarity in the leaf vasculature features is mainly on account of large leaves both in gleichenioid ferns (exceptions are the members of Gleichenia s.s.) and in P. wallichiana. Pinnae traces in the gleichenioid ferns are also extra- marginal and are given off from the side of the crescent. In P. vittata and P. w• the pinnae traces are extra-marginal. In the former, however, the pinna trace arises submarginally whereas in P. wallichiana the pinna trace arises from the bulged region behind the invagination which is comparable with the pinna trace in Lophosoria (cf Bower 1923). Bower (1926) considered extra-marginal pinna trace as derived and characteristic of ferns with large ieaves. The role of marginal and submarginal protoxylem elements in constituting the pinna trace is evident. In species with marginal leaf traces only marginal protoxylem elements participate whereas in P. vittata most of the submarginal protoxylem elements build the pinna trace. Although pinna trace in P. wallichiana is partly derived from the bulged region of the vascular bundle and partly from the marginal flap of that side, only protoxylem elements of these parts are used in the formation of extra-marginal pinna trace, a situation comparable with some species of Hypolepis (unpublished data).

Acknowledgement

This work was partly financed by the University Grants Commission, New Delhi.

References

Bower F O 1923 The Fertt~ volume I (Cambridge: University Press) Bower F O 1926 The Ferns volume 2 (Cambridge: University Press) Chandra S and Nayar B K 1970 Some aspects of the morphology of the rhizome of Pteris wallichiana; Proc. Indian Acad. Sci. B71 79-85 Chrysler M A 1943 The vascular structure of the leal of Gleichenia. I. The anatomy of the branching regions; Aro. J. Bot. 30 735-743 Chrysler M A 1944 The vascular structure of the leaf of Gleichenia. II. The petiolar bundle; Aro. J. Bot. 31 483-491 Davie R C 1918 A comparative list of fern pinna traces with some notes on the leal trace in the ferns; Ann. Bot. (London) 32 235-245 Vascular morphology of stipe and rachis in Pteris 407

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