Cruickshank, RH

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PAP. & !'ROC. RoY. Soc. TASMANIA, VoL. 87 (15TH AUGUST, 1953) Chromosome Numbers in the Genus 'Pimelea' By R. H. CRUICKSHANK Department of Botany, University of Tasmania WITH 4 TEXT FIGURES SUMMARY Chromosome numbers in 14 species of Pimelea were determined. A polyploid series with basic number x = 9 exists in the genus. Cytological examination has shown that P. lindleyana is specifically distinct from P. spathulata. INTRODUCTION In Tasmania the genus Pimelea is represented by about 18 species of which 6 are endemic. In most cases separation of the species is easy on classical morphological lines. However, the group of forms allied to P. linifolia have been variously treated by the earlier taxonomists. This cytological investigation was started in order to see if the confusion which existed between P. spathulata, P. lindleyana, P. linifolia, &c., could be resolved. EXPERIMENTAL METHODS For somatic chromosome counts, divisions in apical meristems and very young leaves were stained in Feulgen (Darlington and LaCour 1947). In all the pubescent species, very careful dissection of th~ macerated and stained buds under the microscope was necessary to obtain preparations free from hairs which interfere with squashing. Some counts were checked on microtomed roots stained in crystal violet. Pollen diameter was measured internal to the exine. Measurements were made of 15 grains from each of 10 plants in a population. RESULTS AND DISCUSSION The chromosomes of the Pimelea species investigated were found to be small, averaging 2·5 microns in length. A comparative study of chromo-some morphology was not possible since the treatments used rarely revealed the centromere constrictions. 13 14 CHROMOSOME NU:V1BgRs IN THE GENUS PIMELEA Table 1 is a summary of the numbers determined. It shows that a polyploid series with a basic number of x == 9 exists within the genus, the mitotic counts being 36, 72, 90 and 108. The diploid remains to be detected. All species examined have fertile pollen and there is no evidence of any apomixis, &c., in the genus. In two dioecious species (both tetra-ploid) the numbers of males and females are approximately equaL A sample of P. fiava from Glenorchy gave 49 males to 51 females, and a sample of P. pau.cifloni from Dunorlan gave 22 males to 17 females. No difference in the chromosome complement between male and female could be detected in either species. Pollen diameter varies from 20·2 to 4~)·5 microns for those species measured. It is not directly related to chromosome number, the 12x species P. drupacea having smaller pollen than most of the 4x species. The close relationship of P. and P. lindleyana is, perhaps, reflected in their pollen diameters. By calculation from the pollen diameter of the 4x species P. spathulcda, the expected diameter of the lOx P. pollen is 49·2 microns which agrees closely with the measured diameter of 49·5. As regards taxonomic treatment of the genus, the cytology shows that P. linclleyana, which was grouped by Rodway with P. l.inifolia, by Bentham partly with P. spathulcda. and partly with P. linifolia (Sm.) should be regarded i:iS a separate species. P. linifolia is probably not a Tasmanian species. As regards general classification of the THYMELAEACEAE. the family is a homogeneous one cytologically. The three genera, Daphne, Edge-worthia and Wikstroemia are reported by Darlington and J am1ki Ammal (1945) all to have a basic chromosome number of 9. The family has been differently placed in the schemes of classification of the Dicotyledons drawn up by the various taxonomists. Engler and Gilg (1924) group the THYMELAEACEAE, and the ELAEAGNACEAE together as a suborder of the MYRTU'LORAE. Since the basic numbers of the ELAEAGNACEAE are 7, 10, 11, 12, 13 and 14, there is no cytological justification for this grouping. For other classifications (e.g., Hutchinson, 1946) the cytolog·ical data appear to be neutral at present. REFERENCES BENTHAM, G., 1873.-Flora Australiensis. London. Reeve. DARLINGTON, C. D. AND J ANAKI AMMAL, E. K., 1945.-Chromosome Atlas of Cultivated Plants. London. Allen and Unwin. DARLINGTON, C. D. AND LA CouR, L. F., 1947.·--The Handling of Chromosomes. London. Allen and Unwin. ENGLER, A. AND GTLG, E., 1924.-Syllabus der Pfianzenfamilien. Berlin. Gebriider Borntraeger. HUTCHINSON, J., 1946.·-A Botanist in Southern Africa. London. Gawthorn RODWAY, L., 1903.-The Tasmanian Flora. Tasmania. Tas. Govt. Printer. R. H. CRUICKSHANK TABLE Chromosome Numbers of 'l'asmanian Pirneleas Chromo-Species fJ. cirwrcu. R. Br. P. c·u.rviflom H.Br. !-'. fiava. R.Br. p_ glauccD R.Br. T'. spathulata Labill. P. /igust;·iana Labill. P. m>uea Labill. P. pauc1'fiora R.Br. P. pygn-wea F.v.M. P. 8Cricea (R.Br.) P. serpUlifolia R.Br. P. humili's R.Br. P, lin ell eyanu. 1\<leissn. P. d-rupacea Labill P. a:.;ifiom F.v.lVI. P. filifo;·mis Hook. P. mill1:gani JYieissn. P. strictu Meissn. Col NJcka Mt. Wellington Dunorlan Launceston Glenorchv M uni um1a Triabunna Campania Colli nsva le Dry Creek Dunorlan Guildford Junction Kirgston Po1't Sorel! l\lt. Lloyd Collinsvale Glenorchv Sandy Bay Dunorlan Launceston James River. Lake Augusta Mt. Arthur King Island Campania Glenorchy Sandy Bay Hastings Hobart Taranna Not collected Not collected Not coHected Not collected some number (2n) 86 Bb 3G 3\i 31) 3() 36 36 36 36 3(} 36 (t[g. 36 36 36 36 86 36 36 36 36 36 72 72 72 (fig. 2) 90 (fig·. 3) 108 (fig, 4 108 Pollen diameter 32·5 3tH) :{4,1 32·5 27·7 20·2 39·2 39,8 15 Hi CHROMOSOME NUMBERS IN THE GENUS PIMELEA Magnification x 1,500 FiGURE I FIGUHE 3 FIG. FIG. FIG. Fw. FIGCRE 4 FlGURC l.~Pincelcn ""''-rr,_uw·w._ Kingston. 2n = 36 (Acetic alcohol - Feulgen) 2.--Pimelea Sandy Bay. 2n = 72 (Acetic alcohol -- Feulgen) :i.--Phnclca 2n ::c 90 (Acetic alcohol --- Feulgen) 4.--Pinu:lea drnpacecL Rd., Hobart. 2n = 108) Root tip, 2BD - C.V.) 

Chromosome numbers in the genus Pimelea

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Chromosome numbers in the genus Pimelea

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