ON THE MORPHOLOGY OF THE CALYCULUS

B y C. Ve n k a t a R ao Department of Botany, Andhra University, Waltair

(Received for publication on July 30, 1962)

I ntroduction

T h e subfamily Loranthoideae of Loranthaceae is characterized by the presence of an annular, toothed or lobed structure below the perianth called the calyculus. The morphological nature of the calyculus has been much discussed and so far no satisfactory explanation has been offered. Roxburgh (1874), Bentham and Hooker (1862-93) and Daiiser (1931) considered it to be equivalent to the calyx. However, some doubt was being felt regarding its equivalence to the calyx because the structure is nonvascular in several genera, e.g., Dendrophthoe (Narayana, 1954), Macrosolen (Maheshwari and Bahadur Singh, 1952), Helkanlhes (Johri, Agrawal and Garg, 1957) etc. Narayana (1955) working on Nuylsia florihunda found that the 3-7 lobed calyculus in this species is vascularised by 5 bundles which depart at the base of the floral stele. Maheshwari, Johri and Dixit (1957) who devoted much attention to morphological and embryological studies in the family conclude: “ while further work is necessary, it now appears likely that the calyculus may represent the calyx".

Other taxonomists, however, disagree with the above view. Eichler (1878) considered it to be an outgrowth of the floral axis. Engler and Prantl (1897) and Engler and Krause (1935) accept this view. Schaeppi and Steindl (1942) drew attention to the fact that the lobing of the calyculus when present does not bear any relation to that of the perianth whorl. Willis (1948) remarks that to consider the calyculus as an outgrowth of the axis is ‘perhaps the safest view’.

However, it is unlikely that a structure which is fed by vascular bundles aiising from floral stele like other floral parts, should be an organ sui generis without any morphology.

The possibility of the calyculus being a reduced or vestigial whorl of bracts of a suppressed lateral branch inflorescence was never sug­ gested because the flowers in Loranthoideae are stalked and individually provided with bracts which are ‘always united to their stalks up to the point of origin of the flower’ (Willis, 1948). O bservations

Loranthaceae is a family which has undergone great specialisation and reduction in vegetative and floral organs in consequence of the para­ sitic habit. The ovules have completely disappeared and in some mem­ bers a structureless mass of meristematic cells arises from the floor of the loculus called the mammelon. The presence of isolated tracheids in this structure in some genera like Dendrophthoe, Amyema and Nuytsia led Maheshwari et al. (1957) to consider it as a reduced placenta] tissue. These authors couid construct a series of stages leading to the formation of mammelon and even to its complete disappearance. The presence of vascular bundles in the calyculus in some genera and their absence in others also indicates that the calyculus is a vestigial struc­ ture. The morphological nature of such an organ cannot be decided by ontogenetic or floral anatomical studies. Only studies in com­ parative morphology and evolutionary trends in the inflorescence and flower of allied families can throw some light on the morphology of the calyculus. Several taxonomists suggested affinities among Loranthaceae, and Santalaceae. Bentham and Hooker (1862-93) place the families Loranthaceae and Santalaceae in the order Achlamydo- sporae of the Monochlamydeae and the family Proteaceae in the adjacent order Daphnales. Likewise Engler and Prantl (1897) and Rendle (1952) place the families in the adjacent orders Santalales and . Recent moiphological, floral anatomical and embryological studies in the three families have brought to light a number of close resemblances among them, particularly between l.oranthaceae and Proteaceae. The flowers are uniformly tetramerous in Proteaceae as they are in Viscoideae of Loranthaceae and in Santalaceae. The flowers occur in threes in Santalaceae and Loranthaceae or they become paired due to the suppression of the central flower. Paired arrangement of the flowers is characteristic of all genera of the subfamily Grevilloideae of the Proteaceae. The flowers in Loranthaceae and Proteaceae are pro­ vided with an elongated perianth which becomes brightly coloured and conspicuous. The tepals are valvate in aestivation. They do not show tapering margins as the perianth parts do in other families but are uniformly thick. When polyphyllous they unite in bud due to the interlocking of marginal hairs (Text-Figs. 2, In Loranthoideae the perianth splits down on one side (Hutchinson, 1959), which feature is quite common in Proteaceae (Text-Figs. 4, 7). The perianth segments in Proteaceae and Loranthoideae become strongly reflexed as the flower opens. In Loranthaceae, Proteaceae and Santalaceae the stamens are equal in number to the tepals and antetepalous. The filaments are adnate to the tepals. The anthers are biloc'ular and introrse and show longi­ tudinal dehiscence. In Loranthoideae and Proteaceae the connectives of the stamens are commonly produced beyond the anthers (Text- Fig. 1). B-io The anther tapetum in all the three families is of the glandular tyt>e and c/tokinesis of the microsporocytes is brought about by simultaneous furrowing. The pollen grains are triangular, oblately flattened, tripo- rate with the germ pores situated at the angles (Erdtman, 1952). They are two-celled at the shedding stage. The embryo-sac in all the three families develops according to the Polygonum type. In Loranlhoideae commonly several megaspore mother cells function. In of the Proteaceae also a large number of functional megaspore mother cells is seen and sometimes more than one megasporc of a tetrad function (Venkata Rao, 1961). Endosperm hausloria are found in Proteaceae and Santalaceae (Manasi Ram, 1957; 1959 a, 1959 Bhatnagar, 1960). In all the three families there arc nectaries which are equal i.n num­ ber to the tepals and alternate to them, or sometimes united into a ring. These have been considered by Haber (1959) and Eames (1961) to be equivalent lo reduced petals in Proteaceae. Eames (1961) remarks: "the nectariferous disc of some genera of Proteaceae (four separate glands i i other genera) is from the evidence of comparative form and anatomy vestigial corolla and this family can no longer be placed in the supposedly primitive Apetalae” . But the present writer has produced arguments why the glands cannot be regarded as morpho­ logically equivalent to petals (Venkata Rao, 1960). In some genera of Proteaceae, Brabeium, and Lamhertia the nectaries are in the form of a small tube or cup surrounding the base of the ovary. This necessitates the presence of an annular meristem inner lo the lepal- sfamen whorl. To say that a ‘gamopetalous corolla' arises inner to an epiphyllous staminal whorl is tantamount to disregarding all morpho­ logical tenets. The nectaries in all the three families, therefore, seem lo be merely nectar secreting outgrowths of the thalamus similar to those of the dichlamydeous flowers and not equivalent to the petals. The flowers in Loranthoideae and Proteaceae show close resem­ blance in anatomical structure. The traces for the perianth segments are organised as 4 or 5 strands from the floral stele. Close to their origin the staminal traces arise as pairs of bundles to the inside of the tepal traces. These run parallel lo each other and to the tepal bundle to varying heights (i.e., the tepal and stamen show congenital concres­ cence). The two staminal bundles fuse together before their emer­ gence into the filament. Such a feature is described by Johri et al. (1957) in Helicanifies and by the present writer in a number of Proteaceae (Venkata Rao, 1960, 1961). (Compare Text-Figs. 2 and 3 with Text- Figs. 16 and 18 of Johri ei at., 1957.) The organization of the staminal trace as a pair of bundles is quite rare in angiosperms and the similarity of this feature in the two families taken in conjunction with other features of resemblance should point to a close affinity between them and to the essential homology of the perianth. However, quite conflict­ ing views have been expressed regarding the morphology of the perianth in the two families. Hutchinson (1959) who regarded the calyculus as a reduced calyx refers to the coloured perianth of the Loranthoideae as the coroJla while in the Proteaceae he described the perianth as the calyx. Eames (1961) who considered the glands in the Proteaccae as reduced petals regarded the coloured perianth in this family as sepals. The close similarity in morphological, histological and anatomical features of the perianth in the two families shows that it is essentially homologous and there is little justification for discriminating it as corolla in one family and calyx in the other. Thus the families Loranthaceae and Proteaceae (ajid Santalaceac to some extent) show resemblances in morphological, histological, anatomical and embryological features which indicate that they are probably derived from common monochlamydeous ancestors. The present studies show that evolution of the inflorescence in the Loran­ thaceae and Proteaceae has progressed along parallel lines. A study of the evolutionary trends in Proteaceae which has not undergone reduc­ tion to such an extent as in Loranthaceae is bound to throw sorte light on the morphology of the calyculus. V, The present writer (Venkata Rao, 1957) has shown that the primi­ tive inflorescence in Proteaceae is a much branched, lax panicle. Two trends of evolution are noticed from such a type; (o) reduction in the number of flowers of the lateral branches to two or one and (b) con­ densation of the inflorescence by reduction of pedicels and/or peduncles either before or after reduction in the number of flowers in the lateral branches. These tendencies arc also noticed in several other angio- spermous families (Eames, 1961) like Palmae (Bosch, 1947; Venkata Rao, 1959), Gramineae, etc. In Amarantaceae, another mono­ chlamydeous family. Bak.shi and Chhajlani (1954) have shown that the condensed spikate inflorescence in some genera is a reduced panicle; the ‘bracteoles’ of the flowers show vestigial remnants of reduced lateral branches. So (he solitary flower is the sole survivor of a lateral branch system. In Malvaceae the solitary flower shows a joint in the stalk. A joint is always suggestive of some suppression (r/., joint in the uni- foliate compound leaf of Citrus and joint in the ‘filament’ of the stamen of Euphorbia). The solitary flower in this family seems to be derived by reduction. The epicalyx which is considered as a whorl of brac­ teoles (Rendle, 1952) or stipules (Willis, 1948) seems to be a whorl of bracts of suppressed flowers, which have become adnate to the pedicel of the surviving flower. Whether a solitary flower is primitive or resultant of reduction from a more complex inflorescence can, therefore, be known only from comparative morphology. Reduction and condensation of the inflorescence have progressed in the whole family of Proteaceae. The present writer (Venkata Rao, 1957) has shown that the paired arrangement of the flowers in Grevil- loideae is the result of reduction of lateral branches. In some genera like and the inflorescence is lax. Condensation of the inflorescence after reduction has led to the formation of heads (PI. 1, Fig. 2) or dense spikes (PI. IL Fig- 6) in several genera. The two trends are particularly well noticed in the tribe Proteeae of Proteaceac which is represented by four genera in Australia and 13 genera in S. Africa. In the Australian section, Slirlitigia shows the nearest Text-Figs. 1-10. Fig. 1. L.s. flower-bud of Paramonus sp., x3. Figs. 2 and 3. T.s. at base and top of flower-bud of virgata, xlO . Fig. 4. Fnower bud of ineissneri, x3. Figs. 5-7. serpylli/olia. Fig. 5. A branch, x^. Fig. 6. A head inflorescence with involucre of bracts, x2. Fig. 7. A flower-bud, x 3. Fig. 8. A branch of pauciflora, x Fig. 9. A branch of Leiicospermum piiheruni, x \. Fig. 10. A branch of puiiclala, Xi. approach to the ancestral paniculate type. The inflorescence is much branched and consists of a number of globular spikes or heads aggre­ gated at the end of a long leafless peduncle (PI. II. Fig. 4). Some reduction has occurred in this inflorescence also because the branch inflorescences are dense and the flowers are sessile. The flowers are individually provided with bracts but these are small and inconspicuous. In Petrophila (PI. 11, Fig. 6) and (PI. II, Fig. 5), the flowers occur in dense cone-like spikes or heads of sessile flowers. In addition to the conspicuous and woody bracts with which the individual flowers are provided there are several series of involucral bracts at the base of the inflorescence. These empty bracts suggest that reduction of the inflorescence has occjrred. The other tendency, namely reduction in the number of flowers of the lateral branches, has occurred in Adenanihos (PI. II, Fig. 7) but this is not followed by condensation. The flowers in this occur singly and these are sparsely scattered on the branch. Each flower is sessile and surrounded at the base by an involucre of 6-8 decussating or imbricating bracts. That the flower is the sole sur­ vivor of a lateral branch is evident by the occasional occurre.nce of two flowers within the involucre.

These tendencies of reduction and condensation run parallel in the South African Proteaceae also. In {F. saligna and F. speciosa) the inflorescences are lax; the flowers are sessile and placed individually in the axil of an inconspicuous bract and open in acropetal succession. In some genera like Diastella, , Leucodendron, Mimetes and Protea the flowers are sessile and aggregated into dense spikes or heads. In Leucospermum (Text-Fig. 9) and Diastella (Text-Figs. 5. 6.) the bracts are inconspicuous; in Leucodendron the bracts are large and woody as in the Australian genera Petrophila and Isopogon. In Mimetes (Text-Fig. 8) and Protea (Text-Fig. 10) they are large and petaloid (PI. 11, Fig. 3). Other S. African Proteaceae show an almost continuous series of reduction in the number of flowers of lateral branches to a single flower. Jn {P. medius and P. sceptrum) the plan of the diflTusely branched paniculate inflorescence is evident (Text-Fig. 11) but reduction has occurred in the lateral branches because each is a head of 4 flowerr. which is surrounded by an involucre of 4 bracts (Text- Fig. 12). In the genus Serniria, S. cygnea, S. knightii, S. elongaia (Text-Fig. 13) and S. fucifolia (Text-Fig. 14) show peduncled condensed spikes or heads each with 20 or more flowers and surrounded by several involucral bracts. In S. adscendens the number of flowers in the branch inflorescence becomes reduced to 10-5. In S. brevifolia the lateral heads are sessile and bear only 4 sessile flowers which are surrounded by 4 involucral bracts as in Paranomus, but the heads are aggregated into a compound head (Text-Fig. 15). In Spatallopsis con/usa (Text- Fig. 16j, the total inflorescence is a panicle; cach lateral branch shows 2-3 sessile flowers which are surrounded by an involucre of four bracts (Text-Fig. 17). The lateral branch itself arises in the axil of a bract which is partly adnate to the peduncle (cf. Loranthaceae). The genus , of which 5 species were examined, is characterised by the pre­ sence of a single flower at the end of cach lateral branch inflorescence in Text-Fios. H-25. Fig. 11. A branch of Paronomus medlus, x^. Fig. 12. A lateral head from the above, X3. Fig. 13. A branch of ehngata, x i . Fig. 14. A branch of Serruria fucifolia, x \. Fig, 15. A compound head pf 5. brevifolla, x3. Fig. 16. A branch of Spalallopsis confusa, x j . Fig, 17. A part of the inflorescence from the above, x3. Fig. 18. A branch of Spatalla pant- Us, x^. Fig. 19. A branch of 5. sehcea, < i. Fig, 20. A flower-bud of S. pant- Us, x3. Fig. 21. Flower-bud of 5. .prac/to, x3. Fig. 22. Open flower of S. ^o/- pini, x3. Fig. 23. A flower of S. molUs, x3. Fig. 24. Involucre of bracts of S. moUis, x5. Fig. 25. T.s. base of the flower of S. molUs, x35. which respect it resembles the Australian Aclenanihos. The lateral branch arises in the axil of a bract and the flowers open in acropetal succession so that the total inflorescence looks like a simple raceme (TeAt-Figs. 18, 19). In S. paniHs (Te\t-F'ig. 20), S. gracilis 21), S. golpini (Text-Fig. 22) and S. sericea each flower is surrounded by four sepaloid involucral bracts. So at a sight the flowers appear like typically dichlamydeou.s, isomerous, bracteate, pedicillate ones; only studies in comparative morphology can reveal the homology of the various organs. In Spaialla mollis (Text-Fig. 23) the base of the flower is surrounded by an involucre of 3 bracts the anterior two of which are partly united (Text-Figs. 24, 25). Thus the numerical relation between the involucral bracts and perianth parts (which is seen in other species of the genus) is disturbed [cf. calyculus and perianth of Loranthoideae).

Tfixr-Fios. 26-29. Evolution of the Loranthoideae type of flower from that of Spatalla type according to the views of the writer, h, bract; c, calyculus;] m, mammelon.

The trends towards reduction of flowers of lateral branch and their aggregation are evident in Loranthaceae also. In Loranthoideae each flower appears to be the sole survivor of a lateral branch as in Spatalla. The flowers seem to be sessile; the flower stalk seems to be the peduncle of the lateral branch with which the bract sometimes unites as in Spalallopsis. We can easily visualise the stages of reduction which lead to the formation of the Loranthoideae type of flower from that of Spaialla; these are represented in Text-Figs. 26-29. Fusion of the involucral bracts, perianth and ovary would give rise to the inferior ovary. Anatomical structure shows that the inferior ovary in this family is of appendicular nature. Remnants of the involucral bracts (whicR have already shown tendency for union in Spatalla) would form the calyculus. Reduction would lead to the disapwarance of vascula­ ture from the calyculus and the disappearance of the ovary and ovules. The vestigial placenta would form the mammelon. [The ovary in Loranthaceae may have been derived from a multicarpeJlary one as Maheshwari el al. (1957) suppose].

S u m m a ry

Features of the close resemblance between Proteaceae and Loran- thaceae are pointed out. A comparative study has been made of the inflorescence in Loranthoideae and 47 species belonging to 10 genera of S. African Proteaceae and a large number of Australian Proteaceae. Assuming that the evolution of the inflorescence in both families pro­ ceeded on parallel lines, the calyculus in Loranthoideae is suggested to be a vestigial whorl of bracts of the suppressed flowers of a lateral branch inflorescence which have become adnate to the inferior ovary.

A cknowledgements

The writer wishes to express his thanks to Prof. A. S. Boughey, Department of Botany, University College of Rhodesia and Nyasaland, Salisbury, for the material of Faurea sp. and to the Director, National Botanic Gardens of S. Africa, Kirstenbosch, Newlands, for the her­ barium material of S. African Proteaceae. The writer is also indebted to Mr. K. Satyanandam of the Botany Department, Andhra Univer­ sity, for some line drawings of the herbarium material and to the Department of Botany, University of Tasmania, Hobart, for the photographs. ,

R e fe r e n c e s

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M a h esh w a ri, p. a n d B a h a d u r S in g h . 1952. Embryology of Mpcrosolen cochin- chinensis. Bot Gaz. 114: 20-32,

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Manasi Ram. 1957. Morphological and cmbryological studies in the family Santalaceae. 1. Comundra umhellata. Phytomorphology 7: 24-35. -----—. 1959 <7. Morphological and embryological studies in the family Santalaceae. 11. Exocarpus with a discussion on its systematic position. Ibid. 9: 4-19.

. 1959 h. Morphological and cmbryological studies in the family Santalaceae. III. Leptomeria R.Br. Ihid. 9: 20-33.

N a ra v a n a, R. 1954. Contribution to the embryology of Dendrophthoe Mart. Ibid. 4: 173-79.

1955. Floral morphology and embryology of Nuytsia florihunda R.Br. Proc. 42nd Indian Sci. Congr. 239-40.

R e n d l e , a . B. 1952. The Classification o f Flowering Plants, Vol. II, Dicotyledons, Cambridge.

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ScHAEPPi, H. a n d St ein d l , F. 1942. Blutenmorphologische und embryologische Untersuchungen an Loranthoideen. Vjschr. naturf. Ges. Zurich 87; 301-72.

Venkata R a o, C. 1957. Cytotaxonomy of the Proteaccae. Proc. Linn. Soc. N.S.W. 82 : 257-71.

-. 1959. Contributions to the embryology of Palmae. 11. Ceroxylinae. J. Indian bot. Soc. 38 : 46-75.

-. 1960. Studies in the Proteaceae 1. Tribe Persoonieae. Proc. nat. Inst. Sci., India 26 B; 300-37.

-. 1961. Studies in the Proteaceae II. Tribes Placospermeae and Conospermeae. Ibid. 27 B : 126-51.

W nxis, J. C. 1948. A Dictionary of the Flowering Plants and Ferns, Cambridge.

E x p l a n a t io n o f P la t e s 1 a n d II

P l a t e I

Fkj. 1. A branch of R.Br. Fio. 2, A tmuKb of serrata C«v. Plate U

Fio. 3. A branch of laurim R.Br. Fig. 4. Part of inflorescencc of longifolia Sm. Fio. 5. A branch of Isopogon anethfolius Knight. Fio. 6. A branch of Petrophila linearis R.Br. Fio. 7. A branch of Adenanthos obovata Labill.

(Figs. 1, 2 X i nat. size; Figs. 3-7. x } nat. size) I I? I