The Taxonomic Significance of Stomatal Distribution and Morphology in EpacridaceaeAuthor(s): Leslie WatsonSource: New Phytologist, Vol. 61, No. 1 (Mar., 1962), pp. 36-40Published by: Wiley on behalf of the New Phytologist TrustStable URL: http://www.jstor.org/stable/2429886 .

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THE TAXONOMIC SIGNIFICANCE OF STOMATAL DISTRIBUTION AND MORPHOLOGY IN EPACRIDACEAE

BY LESLIE WATSON

Botany Department, University of Manchester

(Received 9 May I96I)

The morphology of stomata has long been regarded as a useful taxonomic criterion but few observations suggest that their distribution and arrangement are ever taxonomically important above the level of species. It has become apparent, however, that in the Epacridaceae the patterns of stomatal distribution are as important taxonomically as the structural peculiarities of the individual stomata.

Although the stomata of the Epacridaceae have been described as exclusively ranun- culaceous (i.e. anomocytic, Solereder, I908; Metcalfe and Chalk, I950), this is not true for all members of the family. In Richea, Dracophyllum and Sphenotoma, all the species examined by me have rubiaceous (i.e. paracytic) stomata, in which each guard-cell is bounded by a single parallel auxiliary cell. This is significant, because the three genera are isolated from the remainder of the family in other important respects, some of which have been discussed previously by Dormer (I945). There is no indication of this in present systems of classification and their status will be considered in detail in a future paper.

Stomata occur on the sepals of at least some members of nearly all the genera. This is somewhat surprising, because the sepals are thin and scarious; but in some cases, such stomata may be non-functional. Stomata when they occur upon scarious foliar members (prophylls, bracts and bracteoles) are distributed as they are upon the sepals of the same plant: when this differs from that of the leaves, it is sometimes possible (e.g. Styphelia trifiora) to observe a more or less gradual transition in stomatal distribution from pro- phylls to foliage leaves. In addition, several species have stomata, which sometimes appear to be non-functional, on the corolla lobes.

The distribution of stomata on foliage leaves, sepals and corolla of species examined is given in the table. The genera are in the order of Bentham and Hooker in the Genera Plantarum, with the two more recent additions, Decatoca and Rupicola, intercalated. The monotypic genus Wittsteinia, placed by' Bentham and Hooker in the Vacciniaceae but since included in the Epacridaceae (Burtt, I948), was also examined. The stomatal type (paracytic or anomocytic) is indicated by cross-headings, and the number of species in each genus is quoted from Bentham and Hooker (I876) in the first column. In the second, third and fourth columns, the presence or absence of stomata on the adaxial and abaxial surfaces of leaves, sepals and corolla is indicated by + and -.

A primary division of the family into two groups, based on ovary and fruit char- acters, was adopted by Bentham (I869) in establishing the- tribes Styphelieae and Epacrideae. Our table shows that this division is confirmed by the patterns of stomatal distribution. The Styphelieae typically possess only adaxial stomata on the sepals, while the Epacrideae usually have only abaxial ones. I am unable to advance any physiological or ecological explanation for this distinction. The sepals are erect and appressed to the

36

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Stomata in Epacridaceae 37 Table i. Distribution of stomata on leaves, sepals and corolla in the Epacridaceae

Tribe Styphelieae Stomata anomocytic

Species Leaf Sepal Corolla Ad. Ab. Ad. Ab. Ad. Ab.

Styphelia Sm. II S. viridis Andr. - + + S. laeta R. Br. - + 4- - - - S. triflora Andr. - + + - - - S. longifiora R. Br. - + + - - - S. tubiflora Sm. - + + - - - S. tenuiflora Benth. - + + - - -

Coleanthera Stschegl. 3 C. myrtioides Stschegl. - + + - -

C. virgata Stschegl. + + - - -

Astroloma R. Br. i8 A. humifusum R. Br. - + + - - - A. xerophyllum Sond. - + + - - - A. baxteri A. Cunn. ex DC. - + + - - -

A. pinifolium Benth. - + + - - - A. ciliatum Druce - + + - -

Constephium Benth. 5 C. pendulum Benth. - + + - - - C. minus Lindl. - + + - - C. preissii Sond. - + + -

Melichrus R. Br. 2 M. urceolatus R. Br. - + + - -

Cyathodes Labill. I3 C. glauca Labill. - + + - - C. robusta Hook. f. - + + - C. tameiameiae Cham. - + + - - - C. parvifolia R. Br. -- + + - - - C. dealbata R. Br. - + + - - - C. empetrifolia Hook. f. - + + - -

Pentachondra R. Br. 4 P. pumila R. Br. - + + + - -

P. ericaefolia Hook. f. - + - + - -

P. involucrata R. Br. - + + + P. verticillata Hook. f. - + + - - -

Trochocarpa R. Br. 6 T. disticha Spreng. - + + - - - T. thymifolia Spreng. - + + - - - T. laurina R. Br. - + + - - -

Brachyloma Sond. 6 B. ericoides Sond. - + + - - - B. daphnoides Benth. - + + - - - B. ci.liatum Benth. - + + - - -

Needhamia R. Br. I N. pumilio R. Br. + +

Lissanthe R. Br. 3 L. sapida R. Br. - + + - + L. montana R. Br. - + + L. strigosa R. Br. - + +

Leucopogon R. Br. I30 L. verticillatus R. Br. + + + L. amplexicaulis R. Br. - + + L. richei R. Br. - + + L. virgatus R. Br. - + +

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38 L. WATSON

Table i (cont'd) Species Leaf Sepal Corolla

Ad. Ab. Ad. Ab. Ad. Ab.

L. albicans Brongn. et Gris - + + - - -

L. melaleucoides A. Cunn. ex DC. - + + - - -

L. fimbriatus Stschegl. + - - - -

L. muticus R. Br. - + + - - - L. esquamatus R. Br. - + + - -

Decatoca F. Muell. (I) D. spenceri F. Muell. - + +

Acrotriche R. Br. 8 A. serrulata R. Br. - + + A. divaricata R. Br. - + + A. ovalifolia R. Br. - + +

Monotoca R. Br. 6 M. elliptica R. Br. - + + M. scoparia R. Br. - + +

Oligarrhena R. Br. I

0. micrantha B. Br. - + +

Cyathopsis Brong. et Gris. I

C. floribunda Brong. et Gris. - + +

Tribe Epacrideae Stomata anomocytic

Epacris Cav. 26 E. grandiflora Hort. ex Paxt. - + + E. alpina Hook. f. - + E. microphylla R. Br. - + - E. longiflora Cav. - + - + + E. obtusifolia Sm. - + - - - E. impressa Labill. - + - - - - E. paludosa R. Br. - + - - - - E. myrtifolia Labill. - + - - -

Lysinema R. Br. 5 L. ciliatum R. Br. - + - - - - L. pungens R. Br. - + - - - - L. conspicuum R. Br. - + - - - - L. fimbriatum F. Muell. - + - - - -

Rupicola Maiden (2)

R. sprengelioides Maiden - + + - -

R. gnidioides Summerhayes - + - - - -

Archeria Hook. f. 5 A. serpillifolia Hook. f. - + - -4- - -

A. traversii Hook. f. - + - + - - A. racemosa Hook. f. - + - + - -

Prionotes R. Br. I

P. cerinthoides R. Br. - + - + - -

Lebetanthus Endl. I

L. myrsinites Endl. - + - + - -

Cosmelia R. Br. I

C. rubra R. Br. + + - + - -

Sprengelia Sm. 3 S. incarnata Sm. + + - + - -

S. monticola (A. Cunn.) Druce + + - + - -

Andersonia R. Br. I9 A. lehmanniana Sond. + + + + - -

A. simplex (Stschegl.) Druce + + +

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Stomata in Epacridaceae 39 Table i (cont'd) Species Leaf Sepal Corolla

Ad. Ab. Ad. Ab. Ad. Ab.

A. parvifolia R. Br. + + + - - - A. caerulea R. Br. + + + - - + A. micrantha R. Br. + + + - - -

Stomata paracytic

Richea R. Br. i8 R. sprengelioides F. Muell. - + - + R. procera F. Muell. - + - + R. gunnii Hook. f. - + - + R. scoparia Hook. f. - + - +

Dracophyllum Labill. c. 25 (i) Eudracophyllum I9

D. sinclairi Cheeseman. + + - + - + D. prostratum T. Kirk + + - + - + D. secundum R. Br. - + - + - + D. kirkei Berggr. + + + + - + D. recurvum Hook. f. + + - + - + D. latifolium A. Cunn. - + + + + + D. squarrosum Hook. f. + + - + - + D. menziesii Hook. f. + + + + - + D. minimum F. Muell. + + D. longifolium R. Br. + + - + - +

(ii) Sphenotoma 6 D. drummondii Benth. + - + D. capitatum R. Br. - + - + D. gracile R. Br. - + - +

Stomata anomocytic

Wittsteinia F. Muell. I W. vacciniacea F. Muell. - + - +

corolla in all the species, so that no functional difference is suggested. The distinction represents a strong tendency for the Styphelieae to produce only adaxial stomata on appressed organs. Most species have the stomata of leaves on the under surfaces only, but a few species of Leucopogon (in the Styphelieae) have only adaxial ones and in them the leaves are small and appressed, and resemble prophylls. Small appressed leaves of species outside the Styphelieae (e.g. Sphenotoma spp.) have abaxial stomata.

The tribe Epacrideae of Bentham includes Richea and its allies, mentioned above. These mostly resemble other members of the tribe in stomatal distribution on the sepals. This, correlated with the similar ovary and fruit, suggests that they are closer to the other Epacrideae than to the Styphelieae. Sphenotoma has been made synonymous with Dracophyllum by some authors (e.g. Bentham, I869), but the genus forms a very natural group, endemic in south Western Australia, and differing from Dracophyllum in many respects. From the table, we see that these differences are reflected in the patterns of distribution of the stomata.

The three genera Cosmelia, Sprengelia and Andersonia stand alone in this tribe in the constant presence of stomata on both leaf surfaces. These are the only Epacrids (exclud- ing Richea and its allies) with sheathing leaves. In addition, the mode of leaf abscission is peculiar in that the cortex of the internode below is shed with the leaf, and there are no leaf-scars on the stems (Dormer, I945). The group is evidently very isolated, although it has not yet been given taxonomic recognition.

In nearly all Epacrids, the leaves have a parallel venation, and in the vast majority the guard-cells of the stomata lie parallel with veins and with the long axis of the leaf. All the species with reticulate venation (e.g. Archeria spp.) also have the guard cells parallel

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40 L. WATSON

with the longitudinal axis of the leaf, except the monotypic Wittsteinia, in which they are randomly orientated. The inferior ovary and a lack of sclerenchyma in the leaf are features peculiar to Wittsteinia, and the species is evidently very distinct from other members of the family. Its true affinities must remain in doubt until further investig- ations are made.

The tiny leaves of the monotypic Needhamia, in which the venation is parallel also have stomata with a random orientation - a feature which emphasizes the isolation of this genus among the Styphelieae.

The genus Pentachondra is unusual among the Styphelieae in that the sepals have abaxial stomata. It has been made synonymous with Trochocarpa (Mueller, 1867), from which it differs in inflorescence and fruit structure, as well as in stomatal distribution. Pentachondra verticillata Hook. f. was provisionally included by Bentham in this genus (I869), but since it differs from the other species in the inflorescence and the fruit, as well as in stomatal distribution, it is certainly incorrectly placed. The fruit and inflorescence are those of Leucopogon, and the species is best included in that genus.

The only other species in the Styphelieae with abaxial stomata on the sepals is the monotypic Oligarrhena, which is also remarkable in having only two stamens in the flower where other Epacrids have four or five; the inflorescence, a terminal compound raceme, is also unique.

In the tribe Epacrideae, Andersonia alone typically has sepals with only adaxial stomata. This supports my opinion that the genus should not be made synonymous with the closely related Sprengelia.

The stomatal distribution pattern, in common with most taxonomic characters, is not an infallible criterion. Thus, the genera Andersonia and Pentachondra undoubtedly belong to the Epacrideae and Styphelieae respectively, although the stomatal position on the sepals would suggest otherwise. Pentachondra ericaefolia is the only species in that genus without stomata on both sepal surfaces; but I have been unable to correlate this with any other fundamental difference. Similarly, the orientation of stomata is usually of importance in the family; but Lysinema conspicuum, although in other respects a perfectly good Lysinema, is to my knowledge the only Epacrid to have stomata arranged transversely across the longitudinal axis of the leaf. Nevertheless, it is true to say that in the Epacridaceae, peculiar orientation or distribution patterns of stomata usually serve to indicate other peculiarities in the plants concerned. Preliminary investigations suggest that similar criteria can be applied with advantage in the Ericaceae.

ACKNOWLEDGMENTS

I wish to thank the Director and the Keeper of the Herbarium and Library at the Royal Botanic Gardens, Kew, for the loan of specimens; and the Department of Scientific and Industrial Research, who provided the studentship under which this work is being car- ried out.

REFERENCES BENTHAM, G. & HOOKER, J. D. (I879). Genera Plantarum, 2, 6o8. Reeve, London. BENTHAM, G. (I869). Flora Australiensis, 4, I42. Reeve, London. BURTT, B. L. (1948). Kew Bull., no. 3, 493. DORMER, K. J. (1945). Morphology of the vegetative shoot in Epacridaceae. New Phytol., 44, I49. METCALFE, C. R. & CHALK, L. (1950). Anatomy of the Dicotyledons, z, 840. Clarendon Press, Oxford. MUELLER, F. (I867). Fragmenta, 6, 74. SOLEREDER, H. (I908). Systematic Anatomy of the Dicotyledons, revised by Scott, D. H., I, 490. Clarendon

Press, Oxford.

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