Observations on the Stomatal Apparatus of () Author(s): John W. Grear, Jr. Source: Botanical Gazette, Vol. 134, No. 2 (Jun., 1973), pp. 151-153 Published by: The University of Chicago Press Stable URL: http://www.jstor.org/stable/2473706 . Accessed: 12/08/2011 09:40

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http://www.jstor.org BOT.GAZ. 134(2) :151-153. 1973.

OBSERVATIONSON THE STOMATALAPPARATUS OF ORONTIUM AQUATICUM( ARACEAE)

JOHN W. GREAR, JR. Department of Botany, University of Toronto, Toronto, Ontario

ABSTRACT The stomatal apparatusof Orontiumaquaticum is confinedto the upper epidermisof the leaf and consists solely of two guard cells, with no accompanyingsubsidiaries. The guard cells, which possess flangelikethickenings of the wall flanking the stomatal pore, are sunken and largely obscuredby the overlapping ordinary epidermal cells. Lysichitum and Symplocarpus, genera closely related to Orontium, also lack subsidiaries.This indicates that the stomatal complex within the Araceae is probably more diverse than was previously thought.

Introduction sentative having four subsidiaries was mentioned, In a previous paper by the author (GREAR1966) although not by name. None of these belongs to the devoted primarily to the cytology and migrational Calloideae of ENGLER,which, in addition to Oron- history of Orontium aquaticum L., mention was tiusn, includes Calla, Symplocarpus, and Lysichi- made of the need for further studies in this mono- tugn. Lysichitu1nwas described as having large typic , especially in connection with various epidermal cells but the number of subsidiaries was aspects of morphology. not indicated. Three general classes of stomatal STEBBINSand KHUSH (1961), in a pioneering apparatus, based upon the number of associated survey of the stomatal complex of a large number subsidiaries, if any, were recognized: Class I, with of monocots, found that genera and even families no subsidiaries, Class II, with two, and Class III, are usually constant in having a characteristic with more than two. \\rith the exception of stomatal complex and that such morphological data e1s isael1za, the Araceae included by STEBBINSand obtained from vegetative portions of a could KHUSHbelong to Class III. Class III was con- be of use in classification. sidered as exemplifying the generalized (primitive) WEBBER(1960) surveyed the epidermal structure condition, Class I the most specialized (advanced), and stomatal apparatus of representativesof a wide and Class II an intermediate condition. The Lem- range of terrestrial Araceae; however, neither naceae, represented by a species of Le1nna,was Orontiusnnor any other member of subfamily Cal- placed in Class I because of the absence of any sub- loideae of the Araceae was included. His survey, sidiaries whatsoever. This is of interest because the based upon representatives of 21 genera, indicated Lemnaceae are generally accepted as representing that stomata may be confined to the lower surface a group derived from the Araceae through reduction of the leaf or may be present on both surfaces. In and simplification (WILSON1960), which would ap- reference to the subsidiaries surrounding the guard pear to have involved not only the vegetative body cells, it was found that the number varied from two and floral features, but the epidermis as well. These to four, six, eight, or more. Finding considerable various considerations prompted the author to variation in the number and arrangement of sub- undertake a special study of the epidermis of sidiaries associated with stomata, WEBBER con- Orontiuan. cluded that no taxonomically significant conclusions could be drawn from these data. Material and methods As mentioned previously, STEBBINSand KHUSH Strips of leaf epidermis from both living and ( 1961) later surveyed and classified variation in specimens, as well as plastic peels of cuticular the organization of the stomatal complex in the dried leaf epidermis of monocotyledonsin general and as- imprints prepared according to the method of SIN_ sessed its value in reflecting phylogenetic relation- CLAIRand DUNN (1961), served as sources of in- ships. These authors did not refer to the work of formation in the analysis of the structure of the WEBBER.They indicated the number of subsidiaries epidermis. These materials were supplemented by surroundingthe guard cells for three named genera transverse freehand sections of leaf blades in the of Araceae: Arisaesna,with twonOieffenbachia, with final interpretation of the structural organization six or seven, and Scindapsis, with eight. A repre- of the stomatal apparatus.

151 152 BOTANICALGAZETTE [JUNE

Results and discussion The lower epidermis of the leaf is devoid of stomata, lacks chloroplasts,and is composed of long, n ': 73 ' somewhat irregular, rectangular cells several times longer than they are broad and oriented in the di- rection of the long axis of the leaf blade. The cells are plain surfaced (nonpapillose). FIG.2. Transverse section of stomatal apparatus of The stomatal apparatus of the upper leaf Orontium aquaticum showing the upper ledgelike thick- epidermis consists solely of two guard cells con- ening of guard cells adjacent to stoma, a portion of taining numerous chloroplasts. The guard cells are papillose upper epidermis, and the palisade parenchyma manifestly depressed below the level of the ordinary (X 340). epidermalcells, which lack chloroplasts.The surface area of a pair of guard cells essentially equals that crypts, in which the liplike wall thickenings of the of a single ordinary epidermal cell. In plastic im- guard cells are centered and so conspicuous as to pressions, the guard cell wall thickenings, simulating resemble entire cells. In reality, however, the sunken whole guard cells, appear in surface view to be sur- guard cells are largely obscured in surface view by rounded by two narrow subsidiaries ( fig. 1) . the overlapping ordinary epidermal cells, which Examination of actual epidermal strips, however, jut out over them (fig. 2). So erroneous was the indicates that this is not the case. The narrowly initial impression of stomatal structure and orga- rectangular depression beneath which the guard nization in Orontiumobtained by means of plastic cells are situated is not itself cellular in organiza- peels alone that it seems appropriate to emphasize tion, although it gives the illusion of being so in the importance of judicious use of the technique plastic peel impressions.This illusion is produced in and its limitations. part by the sunken position of the guard cells and The ordinary cells of the upper epidermis are in part by the flangelike thickening of the guard cell scarcely longer than they are wide, their dimensions wall flanking the stomatal aperture.These flangelike essentially equaling the width of the cells of the or hingelike projections can best be seen in sectional lower epidermis. The stomata are interspersed view, where they appear as horns or ledges (fig. 2). among these cells at frequent intervals, usually no Orontiumexhibits only an upper ledge on each of more than two to four ordinary epidermal cell- the guard cells, whereas the guard cells of some widths apart. The ordinary epidermal cells are exhibit both an upper and a lower ledge conspicuously papillose, each with its convex walls (ESAU1953). The long axis of the stomatal depres- forming a conspicuous mammose contour (fig. 2). sion as seen in surface view is oriented in the same In plastic peels, these papillae appear in surface direction as the long axis of the guard cells and view as circular optical expressions under magnifi- their conspicuous thickened wall ledges. The stoma- cation, the diameter of which varies with the depth tal depressions thus appear as slitlike cavities or of focus. The height of these outer surface con- vexities essentially equals, or is somewhat less than, the depth of the anticlinal walls. Air, entrapped between the papillae and/or in the stomatal de- pressions of the upper epidermis, may be the cause of an iridescent sheen observed when the leaves are submerged. The under surface of the leaf epi- dermis, composed of nonpapillose cells, does not exhibit this sheen on submergence. It is clear that the stomatal apparatus of Oron- tium lacks subsidiaries. Thus, all three of STEB_ BINSand KHUSH'Sclasses of stomatal organization are representedby the Araceae. Insofar as is known, this is the first report of a member of the Araceae having no subsidiary cells associated with the sto- mata. The significance of this finding is not at all FIG. 1. Pattern of upper leaf epidermis of Orontium clear, although the condition is not unknown in the aquaticufilas obtainedby means of plastic peel. The dotted lines represent the obscured portion of the guard cells, Arales. Absence of subsidiaries is also the case which are sunken below the level of the epidermis in in Lemna (Lemnaceae), as previously indicated. surface view ( X 340)- Whether or not the absence of subsidiaries is to be 1973 GREAR STOMATALAPPARATUS OF ORONTIUM 153 expected in highly derived plants, such as Lemna epidermalstructure, sharing a similar large cell and Orontium, is at this point a matter of specu- size. lation. It is clear, however, that no correlation STEBBINSand KHUSHpointed out that the fami- exists between the aquatic habit and the absence lies Araceae, Lemnaceae, Palmae, Pandanaceae, of subsidiaries, for many terrestrial monocots are and Cyclanthaceae,which comprisethe orderSpa- known to lack them. diciflorae of ENGLERand GILG ( 1924), agree, In this connection, a cursory examination was with the exceptionof the Lemnaceae,in having made of the epidermis of herbariumsamples of the stomatal complexeswith many subsidiaries.They allied genera Lysichitum and Symplocarpus. The also state that these families agree in having epi- following descriptive information was obtained. dermal cells of a small size, except for certain Stomata are present on both upper and lower sur- probablyhighly evolvedgenera within the Araceae, faces of the leaves of both genera. Subsidiaries do such as Lysichitum andArisaema. In view of the ex- not appear to be associated with the stomatal ap- ceptions mentioned,together with the absence of paratus, the cells adjacent to the guard cells being subsidiariesin Orontium, Symplocarpus, and Lysi- of the same size and form as the ordinary epidermal chitum, and the large size of the epidermalcells cells. The structure and sunken position of the in these genera also, it may prove instructiveto stomatal apparatus appear to be essentially the extend the survey of araceous members,among same in both genera and to be essentially similar which the Calloideae appear critical. It seems to those of Orontium. The pattern of the ordinary likely that a comprehensivesurvey may derive epidermal cells of the lower leaf surface of Oron- greater taxonomic significancefrom comparative tium, consisting of long rectangular cells, is dis- epidermalstudies than had previouslybeen sup- posed. similar to that found in Lysichitum and Symplo- carpus, where the cells are more isodiametric in Acknowledgment surface view. With the exception of the unique The author thanks Dr. JAMESE. CRUISE,Uni papillose upper leaf surface in Orontium, the three versity of Toronto, for his critical review of the genera are otherwise quite comparable in their manuscript.

LITERATURE CITED ENGLER,A., and E. GILG. 1924. Syllabus der Pflanzen- organization of the stomatal comples in the leaf epi- familien.Borntraeger, Berlin. dermis of and its bearing on their ESAU, K. 1953. Plant anatomy. Wiley, New York. phylogeny.Amer. J. Bot. 48:51-59. GREAR,J. W., JR. 1966. Cytogeography of Orontium WEBBER,E. E. 1960. Observationson the epidermalstruc- aquaticum(Araceae) . Rhodora68: 2 5-34. ture and stomatal apparatus of some members of the SINCLAIR,C. B., and D. B. DUNN. 1961. Surface printing Araceae.Rhodora 62: 251-258. of plant leaves for phylogenetic studies. Stain Technol. WILSON,K. A. 1960. The genera of the Arales in the 36: 299-304. southeastern United States. J. Arnold Arboretum 41: STEBBINS,G. L., and G. S. KHUSH. 1961. Variation in the 47-72.