Chromosome studies on African plants . 9 . Chromosome numbers in Ehrharta ( Poaceae : Ehrharteae )

Cytogenetic studies of 53 specimens of 14 species of the genus Ehrharta Thunb. confirmed a basic chromosome number of 12 for the genus. Chromosome numbers for 13 species are described for the first time. The highest ploidy level yet observed in the genus (2n = lOx = 120) is reported for E. villosa var. villosa. B chromosomes were observed in several specimens of four different species.


INTRODUCTION
The presentation of chromosome numbers in this report continues with the format established in the first publication in this series (Spies & Du Plessis 1986).However, contrary to previous publications in this series which all dealt with several different genera of the family Poaceae, this paper covers the single genus, Ehrharta Thunb.The results presented here are limited to the species from the winter rainfall area of southern Africa.
The winter rainfall region of southern Africa, with its Mediterranean climate, is located in the extreme south west of the continent.Though small in area, less than 4% of the total land surface of southern Africa, it is floristically extremely important, being recognized as one of the six Floral Kingdoms of the world (Goldblatt 1978).The flora of the Cape Floristic region, or Fynbos Biome, is unique in many respects, being particularly rich in species (Goldblatt 1978), with high levels of endemism.Thus, in the 87 244 km: of the Cape Region (Fynbos and Succulent Karoo Biomes combined), there are over 8 000 species of which 73% are endemic (Gibbs Russell 1987).High species diversity characterizes this fynbos vegetation (Gibbs Russell 1987) and this is also the case with the grasses of this biome.Although rela tively inconspicuous in this vegetation, the fynbos grasses are particularly interesting as many of them are restricted to this region and are poorly known taxonomically.
Ehrharta is one of the grass genera with a high propor tion of its species endemic to the Fynbos Biome.All but three of the southern African species are endemic to the Fynbos Biome (Gibbs Russell pers.comm.).The genus belongs to the tribe Ehrharteae Nevski and, as currently classified, is represented by 30 species (with 16 infra specific taxa) in southern Africa (Gibbs Russell & Ellis 1987).Gibbs Russell & Ellis (1987) subdivided the South African representatives of the genus into seven species groups, i.e. the Setacea, Capensis, Erecta, Calycina, Villosa, Ramosa and Dura groups.The higher classification of the tribe Ehrharteae, which has been reviewed by Gibbs Russell & Ellis (1987), is still unre solved.Most recently Clayton & Renvoize (1986) in cluded the tribe in the subfamily Bambusoideae.How ever, both Soderstrom & Ellis (1987) and Kellogg & Campbell (1987) excluded it from the Bambusoideae, to which they considered the Ehrharteae to be a sister group.
The aim of this study was to determine the chromo some numbers and the meiotic chromosome behaviour of as many different species as possible.Future studies will determine whether this information can contribute to the delimitation of species in the genus, as well as to clarify ing the position of the Ehrharteae in the Poaceae.

MATERIALS AND METHODS
The material used during this study was collected and fixed in the field.A list of the material used and the localities are listed under results.Voucher herbarium specimens are housed in PRE.

DISCUSSION
According to Watson et al. (1986) the basic chromo some number of the genus Ehrharta is 12 and ploidy levels vary from diploid to tetraploid.This study con firms the basic chromosome number but increases the range of polyploidy from diploid to decaploid.In order to place the cytogenetic results in a taxonomic context, the results are discussed according to the species groups of Gibbs Russell & Ellis (1987).
Both species studied in the Capensis subgroup of the Capensis group, i.e.E. barbinodis and E. capensis, were diploid with no meiotic abnormalities (Figure 1A).This is the first reported chromosome number for both species.
The described diploid and tetraploid levels in the Erecta group (Parthasarathy 1939;De Wet & Anderson 1956;Tateoka 1965;Raven et al. 1965 With the exception of E. erecta var.natalensis, of which only one specimen has been studied, the four other taxa of the group have both diploid and tetraploid specimens.E. triandra and E. longiflora are closely related and have many morphological similarities, with E. longiflora being larger than E. triandra.However, since both spec ies have been shown to have diploid and tetraploid popu lations, this size difference cannot be attributed to differ ent ploidy levels. The Calycina group was the most thoroughly studied with counts from 45 plants, representing six of the seven taxa.Both diploid (84%) and tetraploid (16%) specimens were observed (Figure 2D-L) which corroborates pub lished results (Parthasarathy 1939;Love 1948;Tateoka 1957;De Wet 1960;Tothill & Love 1964;Spies & Du Plessis 1986;Hoshinso & Davidse 1988;Spies & Voges 1988).The polymorphic E. calycina diploid forms in clude prostrate coastal plants with short, broad leaf blades as well as the very common, widely distributed plants with erect growth habit and flat leaf blades.The tetraploid form of E. calycina seems to be restricted to densely tufted plants with erect, narrow, often rolled leaf blades.The chromosome numbers reported here for E. brevifolia var.brevifolia and E. brevifolia var.cuspidata (Figure 2A-C), as well as E. delicatula and E. melicoides, are the first reported numbers for the taxa.
A very high frequency of specimens from the Calycina group were aneuploid (24%) with one or two additional chromosomes, although most had two.With the excep tion of one E. brevifolia var.brevifolia specimen, these additional chromosomes were restricted to E. calycina.Love (1948), Tothill & Love (1964) and Spies & Voges (1988) have previously reported one to six additional chromosomes beyond the basic complements) in E. ca lycina.Tothill & Love (1964) referred to these additional chromosomes as supernumerary chromosomes and Spies & Voges (1988) called them B chromosomes.Both groups of authors observed no size or behavioural differ ences between the additional and standard chromo somes.As in these three previous studies, we observed meiotic irregularities, including late disjunction of bivalents during the first division (Figure 2L) and non-align ment of chromosomes on the metaphase plate (Figure 2J).As was also observed in these previous studies, the extra chromosomes may sometimes pair, either as multivalents or as bivalents (Figure 2F).Additional abnorma lities observed during meiosis include the presence of univalents in a diploid specimen Davidse 33371 (n = 12) and up to six anaphase I laggards in Davidse 33321 (n = 24) (Figure 2L).
A very narrow spindle on one side of the cell was observed in an E. delicatula specimen (Davidse 33285) (Figure 3A & B).Specimens of both E. brevifolia and E. delicatula had two chromosome pairs associated with the nucleolus (Figure 2A & B).
Only one specimen of the Villosa group was successfully analysed.This specimen, Spies 3 5 0 5 (E. villosa var. villosa), provides the first chromosome number report for a member of this group and it proved to have the highest ploidy yet described in the Ehrhar teae, i.e. n = 60 (Figure 4A & B).Apart from a few multivalents and univalents observed in this specimen, meiosis in this decaploid was normal and no laggards were observed, which is surprising in view of the high ploidy level.

FIGURE 1.-Meiotic chromosomes in:
A, the Capensis subgroup, E. capensis, Spies 3168, metaphase I with 12 bivalents; B, the Erecta group, E. triandra.Davidse 33320, diakinesis with 12 bivalents of which four are associated with the nucleolus, x 1300.Three specimens of the Ramosa group were counted and the counts represent the first chromosome number reports for these species.The E. ramosa subsp.ramosa specimen was a normal diploid plant (Figure 5A & B).The E. rehmannii subsp.rehmannii specimen was a diploid with 0 -5 B chromosomes (Figure 5C -E).During metaphase I the B chromosomes were indis tinguishable from the euchromosomes but at the end of anaphase I they seemed to despiralize (Figure 5D).It seems as if the division of these normal bivalents into chromosomes and the division of the univalents into chromatids is not synchronized.The E. rehmannii subsp.subspicata specimen had the second highest ploidy level found in the Ehrharteae, with n = 36.A low frequency of multivalents (up to hexavalents) were ob served in this subspecies (Figure 5F  • ' up to six univalents were observed during diakineses.No laggards were observed in this specimen at anaphase I and the rest of meiosis was normal. The only representative of the Dura group studied, was a diploid E. dura specimen with a B chromosome present in approximately 90% of the cells studied (Figure 6A-C).The B chromosome appears as a round, lightly stained body during diakinesis (Figure 6B).It is present in all stages and during telophase I it is excluded from the nucleus (Figure 6C).
In summary, the basic chromosome number of the genus Ehrharta is 12 and ploidy levels range from di ploid to decaploid.Based on one earlier count for one specimen of E. calycina with 2n=30, Spies & Voges (1988) suggested that a basic chromosome number of six is possible.However, the current, much more extensive results, indicate that the 2n=30 plant is probably an aneuploid with six additional chromosomes.It is also interesting to note that ploidy levels exceeding tetraploidy, were restricted to the eastern part of the distribution area of the genus.Further cytogenetic studies on Ehr harta should include the production of artificial hybrids between the different species and meiotic analyses of these hybrids to clarify the genomic relationships in the genus.
FIGURE 3.-Meiotic chromosomes in the Calycina group: A & B, E. delicatula, Davidse 33285, with 12 bivalents and a very dis tinct and narrow spindle, which may be off-centre, B, x 1100.