304 S.-Afr.Tydskr. Plantk. , 1989,55(3): 304-309 An SEM study of the external pollen morphology in Senecio and some related genera in the subtribe Senecioninae (Asteraceae: Senecioneae) P.L.D. Vincent* and F.M. Getliffe Norris Charles E. Moss Herbarium, Department of Botany, University of the Witwatersrand, P.O. Wits, Johannesburg, 2050 Republic of South Africa and National Botanic Gardens, Kirstenbosch, Clrivate Bag X7, Claremont, 7735 Republic of South Africa Accepted 7 February 1989 The external pollen morphology of 95 species of the genus Senecio, predominantly from southern Africa, and 11 species from related genera of the subtribe Senecioninae, was investigated using the scanning electron microscope. The pollen of all the species studied is spheroidal, uniformly tricolporate and echinate. The distal ends of the spinules are entire and their apices are acute. Only the frequency of the spinules and the length: basal width ratio of the spinules varied amongst the species studied. Die eksterne stuifmeelmorfologie van 95 Senecio-spesies, oorwegend van Suider-Afrika, en 11 spesies van verwante genusse van die subtribus Senecioninae, is met behulp van die aftaselektronmikroskoop ondersoek. Die stuifmeelkorrels van al die ondersoekte spesies is sfero'idaal, eenvormig trikolporaat en stekelrig. Die distale onvertakte punte van die stekels is skerppuntig. Slegs die frekwensie van die stekels en die lengte: basalebreedte-verhouding van die stekels varieer by die ondersoekte spesies. Keywords: Pollen morphology, SEM, Senecio, Senecioninae *To whom correspondence should be addressed Introduction degree of elaboration of the foot layer of the ectoexine' Unlike many other families, knowledge of the pollen (Jeffrey et al. 1978) . morphology of the Asteraceae has been derived predom­ inantly through light microscope studies (e.g. Stix 1960) Materials and Methods and transmission electron microscope (TEM) studies The external morphology of the pollen from each of the (e.g. Skvarla & Turner 1966a, b), there being relatively species investigated in this study (Table 1) was investiga­ little SEM data. The SEM data of Asteraceae pollen has ted using SEM. In most instances one specimen of each been provided mostly by Jeffrey et al. (1978), Skvarla et species was sampled. at. (1977) and Blackmore (1984). Pollen was obtained from unopened florets of herb­ In studies on the generic limits of Senecio, partially arium specimens, so avoiding the possibility of stimulated by the research of Jeffrey et al. (1978) and contamination with pollen from unknown species. Jeffrey (1980), it was decided to investigate the external Unacetolysed pollen grains were mounted directly onto pollen morphology of 95 Senecio species and 11 species stubs using double-sided sellotape, sputter-coated with from related genera (Table 1) in the subtribe Senecion­ gold/palladium (Polaron SEM coating unit E5100) and inae. The purpose of this investigation was to ascertain viewed using a Jeol JSM-T200 scanning electron whether there were characters of the external pollen microscope. morphology which would facilitate the elucidation of the Data on the following characters were recorded: generic limits of Senecio. Studies aimed at elucidating (1) Shape of pollen grain, using the terminology of the generic limits of Senecio, using micromorphological Erdtman (1969) . features, are already under way (Vincent & Getliffe (2) Spinule frequency. 1989). (3) Length:basal width ratio of the spinules. Included in the taxonomic scheme for investigating the (4) Prominence of the colpi. Senecio complex on a world-wide basis (Jeffrey et al. The spinule frequency was determined from the aver­ 1978), was the appearance of the pollen grain surface age of three measurements of the interbasal distance and of the wall stratification. The initial SEM studies by between spinules of the intercolpoid region, using SEM Jeffrey et al. (1978) of some species within the Senecio contact prints of similar-sized pollen grains magnified to complex, revealed that the pollen grains of Senecio are the same degree. An interbasal distance of 1,7 fLm or 'uniformly tricolporate and echinate and vary only in the more constitutes the category 'relatively low frequency', number, density and length:breadth ratio of the spines, while an interbasal distance of 1,0 fLm or less constitutes and in the degree of prominence of the colpi.' Only the the category 'relatively high frequency'. aforementioned variable features noted by Jeffrey et al. The length:basal width ratio of the spinules was deter­ (1978) were included in the present study. Other studies, mined from the average of three measurements of using TEM, have shown that the pollen grain walls 'vary spinules of the intercolpoid region , using SEM contact in thickness and structure, particularly in development prints of similar-sized pollen grains magnified to the and length of the columellae and in the thickness and same degree. S.Afr.J. Bot., 1989,55(3) 305 Table 1 The list of the species and varieties of Table 1 Continued Senecio and related genera included in this study. Also provided are the data obtained from SEM observations Score ratio of the pollen of all the species investigated, with respect to the four pollen characters studied. Note that subse­ Character 2 Character 3 quent to the completion of this study, the names of a S. haygarthii Hilliard 0.83 number of species have changed. The currently S. heliopsis Hilliard & Burtt 1.00 accepted names are provided in parentheses. S. helminthioides (Sch. Bip.) Hilliard 0.92 Characters studied: character 1: shape of the pollen S. hieracioides DC. 1.11 grains; character 2: spinule frequency; character 3: S. hirsutilobus Hilliard 0.92 length:basal width ratio of the spinules; character 4: S. hypochoerideus DC. 1.09 prominence of the colpi. Note that characters 1 and 4 S. inaequidens DC. 0.82 are invariable and consequently are not reflected in the S. ingeliensis Hilliard 0.92 Table. Character 1: all pollen grains spheroidal; charac­ S. inornatus DC. 0.93 ter 4: all pollen grains with prominent colpi. S. juniperinus L. f. 0.91 Character state scores: character 2: 1 relatively = S. latifolius DC. 1.00 high; 2 relatively low (see text for definition) = S. lydenburgensis Hutchinson & Burtt Davy 2 1.00 S. macrocephalus DC. 1.20 Score ratio S. macrospermus DC. 1.00 Character 2 Character 3 S. madagascariensis Poi ret 0.73 S. mauricei Hilliard & Burtt 1.00 Natal Senecios S. medley-woodii Hutchinson 0.71 S. achilleifolius DC. 0.90 (inc. sed., fide Jeffrey 1986: 934) S. affinis DC. 1.00 S. microglossus DC. 0.82 S. albanensis DC. vaT. doroniciflorus S. mikanioides Otto ex Harvey 0.77 (DC.) Harvey 1.00 (Now Delairea odorata Lem. , fide S. anomalochrous Hilliard 0.93 Jeffrey 1986: 933) S. arabidifolius O. Hoffmann 0.80 S. mooreanus Hutchinson 1.08 S. asperulus DC. 1.00 S. natalicola Hilliard 1.22 S. barbatus DC. 1.00 S. ngoyanus Hilliard 0.90 S. barbertonicus Klatt 0.73 S. othonniflorus DC. 0.88 S. brachypodus DC. 1.00 S. oxyriifolius DC. 1.10 S. brevidentatus M.D. Henderson 1 0.91 S. paludaffinis Hilliard 0.92 S. brevilorus Hilliard 2 0.88 S. panduriformis Hilliard 0.60 S. bupleuroides DC. 0.92 S. pleistocephalus Spencer Moore 1.00 S. cathcartensis O. Hoffmann 0.75 S. polyanthemoides Sch. Bip. 2 1.00 S. caudatus DC. 1.00 S. polyodon DC. S. chrysocoma Meerburgh 1.00 vaT. polyodon 1.00 S. cissampelinus (DC.) Sch. Bip. 1.17 vaT. subglaber (0. Kuntze) (Now Mikaniopsis cissampelina (DC.) Hilliard & Burtt 1.00 C. Jeffrey, fide Jeffrey 1986: 879) S. poseideonis Hilliard & Burtt S. consanguineus DC. 0.89 radiate form 1.10 S. coronatus (Thunberg) Harvey 1.25 discoid form 0.90 S. deltoideus Lessing 1.09 S. sp. aff. S. poseideonis 1.00 S. discodregeanus Hilliard & Burtt 0.86 S. praeteritus Killick 1.18 S. dregeanus DC. 1.50 S. pterophorus DC. 0.92 S. erubescens Aiton S. purpureus L. 0.75 vaT. erubescens 1.00 S. radicans (L.f.) Sch. Bip. 0.67 vaT. crepidifolius DC. 0.79 S. retrorsus DC. 0.93 vaT. incisus DC. 0.64 S. rhomboideus Harvey 0.77 vaT. dichotomus DC. 1 0.90 S. rhyncholaenus DC. 0.83 S. fulgens (J.D. Hooker) Nicholson 2 1.00 S. sandersonii Harvey 1.18 (Now Kleinia fulgens Hook. f. , fide S. saniensis Hilliard & Burtt 0.77 Jeffrey 1986: 935) S. scitus Hutchinson & Burtt Davy 0.92 S. gerrardii Harvey 1.00 S. seminiveus Wood & Evans 0.83 S. glaberrimus DC. 1.08 S. serratuloides DC. 0.71 S. glanduloso-lanosus Thellung 0.90 S. skirrhodon DC. 0.75 S. glanduloso-pilosus Vol kens & Muschler 0.82 S. speciosus Willdenow 1.13 S. harveianus MacOwan 0.60 S. sp. aff. S. speciosus 1.33 S. hastatus L. 2 0.85 S. subcoriaceus Schlechter 0.69 306 S.-Afr.Tydskr. Plantk. , 1989,55(3) Table 1 Continued Results The data of the four pollen characters recorded for each Score ratio of the species investigated, are provided in Table 1. Character 2 Character 3 Shape of pollen grains S. subrubriflorus O. Hoffmann 0.82 All the species studied (Table 1) , have spheroidal pollen S. tamoides DC. 0.92 grains (Erdtman 1969) (Figure 1). (inc. sed. , fide Jeffrey 1986: 934) S. tanacetopsis Hilliard 1.15 Spinule frequency S. transvaalensis Bolus 1.15 The conical-shaped spines forming the echinate appear­ (Now Emilia transvaalensis (Bolus) ance of the intercolpoid regions of the exine of the pollen C. Jeffrey, fide Jeffrey 1986: 919) grains are here termed spinules, since they are always S. umgeniensis Thellung 1.10 shorter than 3 fLm (Erdtman 1969). S. urophyllus Conrath 1.08 The majority of the species studied (Table 1), had a S. variabilis Sch. Bip. 1 0.64 relatively high frequency of spinules (Figure 1), while S. viminalis Bremekamp 2 0.91 the following 10 species had a relatively low spinule Cape heterochromous non-yellow (purple) Senecios frequency: S.