1956 1
Chromosome Numbers in Transvaal Grasses J. M. J. de Wet and L. J. Anderson Divisionof Botany,P. O. Box994 , Pretoria,South Africa Received August 11, 1955
The family Gramineae is very well represented in South Africa , but very little work has been done on their cytology . This investigation represents the third in a series (de Wet 1954 a, b) on the chromosome numbers of South African grasses. Many of the chromosome numbers require little comment and are listed mainly to get them on record . A few are more important and will be discussed in detail . The genera investigated are classified according to Hubbard (1934) and Pilger (1954). This makes it possible to correlate the cytological observations with purely morphological data.
Material and methods The majority of the species have been collected in the veld and were identified by Mr. J. A. Anderson of the South African National Herbarium . Seed of Phyllorachis sagitata Trimen were received from the Department of Botany, University of Pretoria. A few species were cultivated on the Prinshof Experimental farm , Division of Botany. Herbarium specimens together with corresponding root tip slides are filed with the Division of Botany at Pretoria. Root tips were fixed in Randolph's (1935) "CRAF" fluid. These were dehydrated, embedded and sectioned in the usual manner. Staining was done according to the method outlined by Stockwell (1934). For a study of leaf anatomy the procedure described by Prat (1948) was followed. Drawings were made with the aid of a camera lucida; the magnifications are indicated.
Results The genera studied are listed and the chromosome numbers reported are summarized in table 1. Festuceae subtribe Festucinae. As was indicated by previous workers the basic chromosome number of Festuca is n=7 and the chromosomes are large. Tetrachne dregei is characterized by a basic chromosome number of n=10 and the chromosomes are smaller than those characteristic of the subtribe Festucinae. Anatomical and epidermal traits of the leaves indicate a closer relationship with the tribe Eragrosteae. Aveneae subtribe Aveninae. Agrostis eriantha has 42 large somatic chromosomes. This is in agreement with previous records indicating a basic chromosome number of n=7 for the genus. Arundinelleae. This tribe is placed by Hubbard (1934) in the neighbour
Cytologia 21, 1956 1 2 J. M. J. de Wet and L. J Anderson Cytologia 21
Figs. 1-57. Chromosome number (2n). •~2800. 1. Festuca scabra, 28. 2. Agrostis eri antha, 42. 3. Tristachya biseriata, 24. 4. Phalaris tuherosa var . Stenoptera, 28. 5. Enneopogon brachystachys, 36. 6. E. cenchroides, 36. 7. E, pretoriensis, 18 . 8. Schnidtia glabra, 36. 9. Phyllorachis sagittata, 24. 10. Eragrostis denudata, 20. 11. E. lappula var, divaricata, 40. 12. Bewsia biflora, 30. 13. Dinebra retroflora, 20. 14, Sporobolus stapflanus, 36. 15. S. fimbriatus, 36. 16. S. nitens, 18. 17. S. smutsii , 36. 18. Mi.cro ch.loa caffra, 20. 19. Aristida curvata, 44. 20. A. diffasa var. burkei, 36 . 21. A, gracilior, 36. 22. A. transvaalensis, 24. 23. Perotis patens, 36. 24. Panicum repens, 36. 25. Brachiaris humidicola, 72. 26. Echinochloa pyramidalis, 54 . 27. Urochloa trichopus, 30. 28. U, mosambicensis, 30. 29. Digitaria diagonalis, 36. 30. D . longiflora, 18. 31. D. litoralis, 18. 32. D. seriata, 36. 33. D. tricholaenoides, 18 . 34. D. valida 36. 35. D. valida var, glauca, 36. 36. Setaria almaspicata, 36. 37, S. lindenbergiana , 36 . 38. S. lindenbergiana, 18. 39. S. perennis, 36. 40. S. phragmitoides, 54 . 41. S . splendida, 54. 42. S. tenuiseta, 36. 43. S. chevalieri, 36. 44, Axonopus suffultus , 40. 45 . Anthephora pubescens, 40. 46. Miscanthidium junceum, 30. 47. Ischaemum arcuatum , 50 . 48. Urelytrum squarosu.m, 20. 49. Chrysopogon montanus var. tremulus, 20 . 50 Dichanthiurn pappilosum, 30. 51. D. aristatum, 40. 52. Cymbopogon prolixus, 40 . 53. Andropogon appendiculatus, 20. 54. A. sehzinzii, 20. 55. Hyparrhenia filipendula, 40 56 . . 1I. filipendula var. pilosa, 40. 57. Trachypogon spicatus, 20. 1956 Chromosome Numbers of Transvaal Grasses 3
Table 1. Classification of the genera and chromosome number of the species
1* 4 J. M. J, de Wet and L. J. Anderson Cytologia 21
Table 1. continued 1956 Chromosome Numbers of Transvaal Grasses 5
Table 1. continued
hood of the Paniceae. It was indicated by de Wet (1954 a) that this tribe represents a stepping stone between the series Phragmitiformes and Panici formes of Avdulov (1931). The genus Tristachya is characterized by small chromosomes and the basic chromosome number is n=12. Leaf anatomy and epidermis is of the Panicoid type (cf. Avdulov, 1931 and Prat, 1936). Moffet and Hurcombe (1944) demonstrated a basic chromosome number of n=10 for this genus. Phalarideae. Two genera included by Pilger (1954) in this tribe have been investigated. The genus Phalaris is typically festucoid in respect to chromosome size and leaf anatomy. Ehrharta on the other hand has n=12 and small chromosomes (Parthasarathy, 1938), the chlorophyll distribution of the leaf is of the Festucoid type (Avdulov, 1931) and the epidermal charac teristic resemble those of the Oryzeae (Prat, 1936). The small chromosomes and a basic chromosome number of n=12, together with the anatomical data suggest affinities with the tribe Oryzeae. Pappophoreae. Avdulov (1931) includes this tribe in his miscellaneous series the Phragmitiformes. Prat (1936) records an Eragrostoid type of epi dermis for the genera Cottea and Pappophorunz, while for species of both genera Covas (1945) reports n=10 and small chromosomes. The genus Enneapogon is definitely characterized by small chromosomes and a basic number of n=9. It was thought by de Wet (1954 b) after counting 2n=36 in Enneapogon scoparius that the basic chromosomes number might be n=12. 6 J. M. J. de Wet and L. J. Anderson Cytologia 21
Enneapogon pretoriensis with 2n=18, however, rule out a basic number of n=12. Schmidtia glabra having 2n=36 indicates that this genus very likely is also characterized by a basic chromosome number of n=9. Anatomical data for the latter two genera are very peculiar. The chlorophyll distribution is of the Festucoid type. The siliceous cells are more or less dumb-bell-shaped and the bicellular haires are more or less club shapped. Thus, also in respect of these two genera, epidermal traits and cytology indicate a closer affinity with the series Eragrostiformes (de Wet, 1954 a) than with the Festuciformes. Because of the Festucoid type of chlorophyll distribution, however, this tribe is included in Avdulov's (1931) series the Phragmitiformes. It is therefore, possible to assume that the series Eragrostiformes could have had its origin in the neighbourhood of this tribe. Phyllorachieae. The genus Phyllorachis is one of the most interesting in the family Gramineae. Trimen (1879), who described the genus, points out that in spikelet structure it resembles the Chlorideae and Phalarideae. The habit of the grass, on the other hand, suggests an affinity with some genera of the Olyreae. Bentham (1881) indicates that the spikelet resembles that of Panicunz, but the fruiting glumes are less hardened. The inflorescence is roughly that of genera belonging to the Chlorideae, but the branches of the panicle are produced beyond the spikelets and the pedicel disarticulates below the glumes. Phyllorachis is treated as a member of the Paniceae by Hackel (1889), who groups it with other genera having heteromorphous or unisexual flowers. Hubbard (1939) studied Phyllorachis and the related genus Humbertochloa. A new tribe, the Phyllorachieae, was described by Hubbard on the basis of this investigation. Hubbard (1939) indicates that the Phyllorachieae differs from the Paniceae, Olyreae and Phalareae in a number of characters. The latter two tribes differ from the Phyllorachieae by their strictly 1-flowered spikelets. The Phyllorachieae differs from the Paniceae in the following salient morphological features. In the Paniceae the spikelets are usually bisexual and similar; the lower lemma is usually thinner than the upper ones; the rhachilla is usually not produced beyond the upper floret; the stamens are 3 or less and the caryopsis, usually, has a punctiform or small basal hilum. On the other hand, in the Phyllorachieae, the lower lemma of the female spikelet is thickened, firmer than the upper floret; the rhachilla is produced beyond the upper floret; the stamens are mostly 6-4 and the caryopsis is characterized by a linear hilum, equaling the caryopsis in length. Anatomical and cytological data similarly suggest that the genera Phyllo rachis and Humbertochloa should be removed from the Paniceae. Phyllo rachis sagitata Trimen and Humbertochloa greenwayi Hubbard were in vestigated. The leaf anatomy of these two genera are very similar. In cross section the parenchymatous outer bundle sheath is poorly differentiated but the mesotome sheath is well developed. Furthermore, the chlorophyll tissue 1956 Chromosome Numbers of Transvaal Grasses 7 is uniformly disposed between the bundles. The internal leaf anatomy is therefore typically of the Festucoid type as described by Avdulv (1931), Prat (1936) and de Wet (1954 a). The Panicoid type, in contrast, is characterized by a well developed outer bundle sheath, a poorly differentiated mesotome sheath and a localization of the chlorophyll tissue around the bundles. The epidermal characteristics are of the Oryzoid type. The siliceous cells are short, dumb-bell-shaped and placed transversely to the axis of the leaf. Long threadlike bicellular hairs are also always present on the ventral surface of the leaves. In respect to anatomical characters the genera included in the Phyllo rachieae resemble the tribe Oryzeae, both in shape and position of the siliceous cells. Avdulv (1931) showed that the angular starch grains of Phyllorachis are similar to those of Oryza except that the individual grains are smaller. Also in respect to gross morphological characteristics the Phyllorachieae can be brought into relationship with the Oryzeae. The elongated hilum and 6-4 stamens resemble the type characters of the Oryzeae. In both tribes also, the number and sexes of their spikelets have sufferred considerable reduction. Cytology similary points to a relation between the Oryzeae and the Phyllorachieae. Ramanujam (1938) indicated small chromosomes and multiples of 12 in the genus Oryza. Phyllorachis sagitata has 24 small chromosomes, which seem to indicate that the basic chromosome number is n=12. The tribe Phyllorachieae, therefore, seems to be very closely related to the Oryzeae. On the basis of anatomical and cytological characteristics it would seem possible to unite these two tribes. Eragrosteae subtribe Eragrostinae. Four genera have been investigated. The basic chromosome number of n=10 reported in the genera Eragrostis, Pogonarthria and Trichoneura is in agreement with earlier reports. A basic chromosome number of n=10 in the genus Bewsia is reported for the first time. Four species of Sporobolus have been investigated. These data indicate a basic number of n=9 in the genus. Chlorideae subtribe Euchloridinae. The genus Microchloa has been studied cytologically by Moffet and Hurcombe (1949). The chromosome number of Microchloa caffra is 2n=20 indicating a basic chromosome number of n=10 for the genus. This is in agreement with the earlier investigation of this genus. Aristideae. It is surprizing that Pilger (1954) should place the Stipeae in the subfamily Festucoideae and the Aristideae in his subfamily Eragrostoideae. These two tribes appear to be closely related and very likely had a common ancestor. Lodicules, stigmas, epidermis and chromosomes, Hubbard (1934), Prat (1936) and Avdulov (1931) all point to a derivation from the primitive Arundineae complex. It is likely, however, that these two tribes originated independently from Arundineae-like forms. 8 J. M. J. de Wet and L. J. Anderson Cytologia 21
The two basic chromosome numbers for Aristida, n=11 and n=12 reported by de Wet (1954 b) have again been encountered. Aristida curvata (2n=44) appears to be a tetraploid on the basis of n=11. The remaining four species have either 2n=24 or 2n=36 indicating a basic chromosome number of n=12. Lappagineae. Only one representative of this tribe, Perotis patens with 36 small chromosomes has been studied. Moffet and Hurcombe (1949) report 2n=40 for the same species. Paniceae. The tribes included by Pilger in his subfamily Panicoideae are in agreement with the classifications of Avdulov (1931) and Prat (1936). The genera Panicum, Brachiaria, Echinochloa, Urochloa, Alloteropsis, Digitaria, Paspalum, Setaria, Cenchrus, Schizachyrium and Axonopus be longing to the tribe Paniceae have been investigated. Krishnaswamy (1940) reported 2n=40 in Panicum repens. The present count, however, indicate 2n=36. This is probably the more acurate count, as the common basic chromosome number for this genus is n=9. Moffet and Hurcombe (1949), however, report basic chromosome numbers of n=8 and n=11, in P. maximum. Krishnaswamy (1940) suggests a basic chromosome number of n=10 and Church (1929) a basic number of n=7 for the genus Echinochloa. It was indicated by de Wet (1954 b) and again in this investigation that the common basic chromosome number for Echinochloa must be n=9. The genus Urochloa has been investigated recording 2n=30 in U. trichopus and U. mosambicensis, thus, having a basic chromosome number of n=10. For the latter species Moffet and Hurcombe (1949) demonstrate 2n=42. The genus Alloteropsis with a basic chromosome number of n=9 has been investigated. For this species Moffet and Hurcombe (1949) count 2n=54. The common basic chromosome number for the genus Digitaria is n=9. Young and Crocher (1933) reported 2n=24 for D. valida var. glauca. The present count reveals 2n=36. Two chromosome varieties of Setaria lindenbergiana are present. The one has an open inflorescense and broad leaves. The other has a more close inflorescense and narrow leaves. The broad-leaf variety which prefers shady places has 2n=36, whereas the narrow leaved variety which grows in open sunny places has 2n=18. The genus Cenchrus is of interest in sofar as Avdulov (1931) reported 2n=34 and 2n=70 in species belong to this genus. The present investigation which is in agreement with that of Moffet and Hurcombe (1949), reveales still a third chromosome number, 2n=36. The basic chromosome numbers observed in the remaining genera are in agreement with earlier reports. Melinideae. Two genera, Rhynchelytrum and Tricholaena were in vestigated. Both genera are characterized by a basic chromosome number of n=9, which is in agreement with an earlier report by de Wet (1954 b) and Moffet and Hurcombe (1949). 1956 Chromosome Numbers of Transvaal Grasses 9
Anthephoreae. The cytology of Anthephora is of interest . A chromo some number of 2n=20 in A. pubescens indicates the presence of a basic number, n=10. Avdulov (1931), on the other hand , reported 2n=18 in A. hermaphrodita indicating a basic chromosome number of n=9 . Andropogoneae subtribe Saccharinae. In contrast to most other systems of classification, Pilger (1954) recognizes two subfamilies, the Panicoideae and Andropogoideae to include the tribes usually classified in the same sub family. Miscanthidium Junceum belonging to the subtribe Saccharinae has been investigated for the first time cytologically. The presence of 30 somatic chromosomes indicates a basic chromosome number of n=10. Andropogoneae subtribe Rottboellinae. The genus Urelytrum with a basic chromosome number of n=10, was previously unknown cytologically. Hermathria evidently has two basic chromosome numbers. Moriya and Kondo (1950) and Ono and Tateoka (1953) indicate a basic chromosome number of n=9. For H. altissima de Wet (1954 b) and the present in vestigation definitely show 2n=20, thus a basic chromosome number of n=10. Andropogoneae subtribe Rottboellinae. Two chromosome-number races are present in Ischaenzunz arcuatumn. For the same species from different localities somatic chromosome numbers of 2n=40 and 2n=50 have been counted. Morphologically these races can not be distinguished the one from the other. Andropogoneae subtribe Sorgineae. The genus Chrysopogon with n=10 has been unknown cytologically. Andropogoneae subtribe Andropogoninae. A basic chromosome number of n=10 in the genera Bothriochloa, Dichanthium, Cymbopogon, Andropogon, Hyparrhenia, Trachypogon and Heteropogon is in agreement with previous records (cf. Myers, 1947). Dichanthium aristatum is characterized by a diploid (2n=20) and tetraploid (2n=40) form. Morphologically the diploid and tetraploid cannot be separated.
Summary The genera investigated were classified according to Pilger and the position of the tribes Arundinelleae, Phyllorachieae, Stipea and Aristideae in this system of classification was critized. The chromosome numbers of 79 species belonging to 45 genera have been counted. Fifty-seven of these species were recorded for the first time, or chromosome numbers differing from earlier counts were reported. The following genera were previously unknown cytologically: -Schnzidtia (n=9); Phyllorachis (n=12); Bewsia (n=10); Miscanthidium (n=10); Urelytrunz (n=10); Chrysopogon (n=10) and Trachypogon (n=10). The inclusion of the genus Ehrharta in the tribe Phalarideae was criticized. It was suggested that this genus should be 10 J. M. J. de Wet and L. J. Anderson Cytologia 21 transferred to the tribe Oryzeae. It was also pointed out that the genus Tetrachne belongs in the Eragrosteae.
Literature cited
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