THE GRASSES (POACEAE/GRAMINEAE) OF THE CAWSTON BLOCK, ZIMBABWE

The Cawston Block is large ranch between 19.8 deg and 19.6 deg S latitude and 28.2 deg and 28.4 deg E longitude in western Zimbabwe near Nyamadlovu and approximately 50 km north of Bulawayo along the south bank of the Umguza river.  Elevations range from ca. 1100m in the north to ca. 1250m in the south with a band along the southern border on a relatively flat plateau and the landforms from there to the river generally a matrix of eroded basalt kopjes with interconnecting basaltic highlands with interspersed lowlands of riverine channels and floodplains down to the river.  Cawston is owned and operated by Peter and Carole Johnstone who provided unfailing and gracious hospitality during the course of this study.

This is a simple floristic treatment of the grass species of the Cawston Block and it is designed to be used for both management and tourism. The species listed here are only those that were identified during the short dry season survey period. Anecdotal reports and "probable" occurrences are not included. It is therefore likely that new species will be added in the future. The list is readily updatable as these occurrences are discovered.

Grasses are a notoriously difficult group due to their very high number of species (ca. 10,000) and tiny floral parts which are so specialized that they require their own vocabulary. Despite the numerous picture books and guides available for grasses, there is no reliable method of determining the true identity of most specimens other than by carefully dissecting the flowers. The terms of most importance (that differ from those generally used for other plants or have a specific meaning in grasses) to be learned before doing this are:

• AWN - A needle like projection from the flower, usually from the tip of a lemma or glume. Heteropogon contortus has a very large, twisted awn from the tip of the lemma.
• FEMALE FERTILE FLORET - A floret that will go on to produce fruit, it always contains a functional pistil but may or may not contain stamens. In Panicum and its allies such as Setaria there is only ever one female fertile floret per spikelet but there is a sterile floret also present below the female fertile one. This sterile floret is reduced to a lemma only and resembles the upper glume. You can tell that it is a sterile lemma by counting the number of bracts outside of the fertile lemma and palea. There will be three. Since there can be only two glumes, and they are always the two lowest bracts, the one closest to the female fertile floret must be a sterile lemma. In Andropogon and its allies such as Hyparrhenia and Bothriochloa there is a different type of floret which may or may not be fertile and may or may not have vestigial sterile female organs but is definitely not both female and fertile. This is the pedicellate spikelet of a basal/pedicellate spikelet pair. The spikelets in this group is always (in our material) found with a female fertile spikelet attached directly to the axis of inflorescence with a second floret that is male or sterile (or both) on a short pedicel coming from the base of the female fertile floret. It is often much smaller than the female fertile floret.
• FLORET - The flower itself. A complete, hermaphrodite, fertile floret consists of (in order, as they are attached to the rachis of the floret) a lemma, a palea, one or more lodicules, one or more stamens, a pistil. Any of these parts except the lemma may be missing. A lemma with none of these parts associated with it is a common type of sterile floret in thegrasses. Several florets may be present, stacked on top of one another in a single spikelet.
• GLUMES - These are the two (sometimes only one) bract at the base of the spikelet. The lower glume is the one attached lower down on the rachis. It is also called the first glume and is sometimes much smaller than the upper glume.
• LEMMA - The bract that encloses the palea and the sexual parts of  the flower. A sterile lemma is one that does not enclose any functional sexual parts. The single fertile floret in Panicum and its allies is subtended by a sterile lemma.
• PALEA - The bract closest to the sexual organs of the floret, it has a lemma inserted below it. It is often thin and translucent and sometimes has 2 keels running down its back.
• RACHIS - This is an axis, in grasses it refers to an axis in the inflorescence. It can be the main upright axis of an entire inflorescence or the tiny piece connecting two pairs of spikelets in a raceme of a raceme pair of a compound panicle. A very small rachis is sometimes called a rachilla.
• SPIKELET - The spikelet is the basic unit of organization in the grass inflorescence. It consists of the glumes (with rare exception there are 2) and everything above them on the same rachis. This is always one or more florets.

Two good reference works to refer to for clarification of identifications or terms are:

Gibbs Russell, G.E., L. Watson, M. Koekemoer, L. Smook, N.P. Barker, H.M. Anderson & M.J. Dallwitz 1990. Grasses of Southern Africa, an identification manual with keys, descriptions, distributions, classification and automated identification and information retrieval from computerized data. Memoirs of the Botanical Survey of South Africa No. 58. van Oudtshoorn, F. 1992. Guide to Grasses of South Africa. Briza Press, Arcadia, South Africa.

The former is an excellent reference work that is nearly complete for Zimbabwe although it is primarily concerned with South Africa (and included countries), Botswana, and Namibia. It is still available from the National Botanical Institute, Private Bag X101, Pretoria 0001, South Africa. The only truly complete work for Zimbabwe will be the Flora Zambesiaca (Crown Agents, London) of which only part of the grass family has been completed. Completed volumes are available from the Kew Botanical Garden, Richmond Surrey, SW1, England, and sporadically from the national herbarium in Harare. The book by van Oudtshoorn is recommended not for its taxonomic treatment, which only comprises a small percentage of the species in Zimbabwe, but for its photographs which are superb. It is available from CNA stores in South Africa or by writing directly to the publisher, Briza Press, P.O. Box 56569, Arcadia, 0007, South Africa.
 

KEY TO THE GENERA
 

1. Spikelets in pairs (or rarely triads) with one basal and hermaphrodite and the other(s) pedicellate and unisexual or sterile. 2
1. Spikelets not in basal/pedicillate pairs. 13
 

2. Spikelet pairs in groups of 1-3 at the tips of the inflorescence branches surrounded by 1 or more sphateate bracts, this giving the appearance of hanging
bells. Themeda triandra
2. Spikelet pairs not as above. 3
 

3. Spikelet pairs in racemes of 3 or more pairs, these racemes may be themselves in pairs at the tips of inflorescencebranches or clustered from a single point. 5
3. Spikelet pairs in an open, branched and rebranched panicle, not grouped into finite racemes. 4

4. Leaf sheath folded to creased or keeled, lense shaped in cross-section. Chrysopogon serrulatus
4. Leaf sheath smooth, round in cross-section. Sorghum

5. Spikelet pairs in short (< 10 cm, usually < 6 cm long) pairs of racemes in a branched open, usually nodding compound panicle. 6
5. Spikelet pairs in one or more racemes clustered (digitate to subdigitate) at the top of the culm. 8

6. Lower glume of the female fertile spikelet 2-keeled or with a clear narrow groove. 7
6. Lower glume of the female fertile spikelet rounded on the back or rarely very slightly grooved near its tip only. 40

7. Awn of the female fertile spikelet 50-100 mm long. Hyperthelia dissoluta
7. Awn of the female fertile spikelet < 12 mm long. Andropogon gayanus

8. Racemes solitary at the tips of branches or at the apex of the culm. 9
8. Racemes in groups of 2 or more at the tips of branches or at the apex of the culm. 11

9. Female fertile spikelets awned. 10
9. Female fertile spikelets unawned. Rottboellia cochinchinensis

10. Awns long (ca. 30-100 mm long), brown hairy. Heteropogon contortus
10. Awns shorter (ca. < 20 mm) not brown hairy. Schizachyrium

11. Racemes in groups of 2-3 (rarely 5) at the apex of the culm, racemes usually > 10 cm long. Ischaemum afrum
11. Racemes in groups of 5 or more (rarely fewer) at the apex of the culm, racemes usually < 10 cm long. 12

12. Pedicellate spikelet hairy, plant with no particular odor, glumes without a pit in the back. Dichanthium annulatum
12. Pedicillate spikelet essentially glabrous (although the pedicel below it will be hairy), plants often with a turpentine odor, glumes sometimes with a small, very obvious pit just above the center of the back. Bothroichloa

13. Lemmas with 3 awns > 5 mm long, joined at their bases, one floret per spikelet. 14
13. Lemmas with a single awn, one or more florets per spikelet (Triraphis has 3 awned lemmas but the 2 lateral awns are inconspiuous and it has 2-5 florets per spikelet). 15

14. Central awn hairy with spreading gray hairs. Stipagrostis uniplumis
14. All awns scabrous to glabrous. Aristida

15. Large reeds over 2 m tall, culm diam often > 1 cm. 16
15. Plants not over 2 m tall, culm diam. never > 1 cm. 17

16. Leaves pungent (with a apical point hard enough to cause injury), inflorescence an open fluffy panicle. Phragmites mauritianus
16. Leaves may be acute but not pungent, inflorescence a compact, spike. Pennisetum purpureum

17. Spikelets subtended by severl bristles, spikelets ovate to round, inflorescence spicate or at least compact. 18
17. Spikelets may be otherwise hairy but not subtended by bristles, inflorescences various. 19

20. Spikelets enclosed in a very hairy flask-like involucre. Cenchrus ciliaris
20. Spikelets only subtended by 1-14, scabrous bristles. Setaria

19. Inflorescence a solitary spike or spicate raceme. 20
19. Inflorescence a panicle, open raceme, or group of racemes. 22

20. Inflorescence a clearly one-sided raceme, the spikelets inserted on only one side of the rachis. Enteropogon
20. Inflorescence cylindrical or multi-sided. 21

21. Major awn of each spikelet longer than the spikelet longer than the length of the spikelet, spikelets packed tightly along the rachis with no spaces between them. Perotis patens
21. Major awn of each spikelet shorter than the length of the spikelet, spikelets not packed tightly along the rachis. Dinebra retroflexa

22. Spikelets with 1 female fertile floret. 23
22. Spikelets with more than 1 female fertile floret. 33

23. Inflorescence made up of numerous racemes either inserted at a common point (digitate) or along the stem racemose). 24
23. Inflorescence an open, spreading panicle. 29

24. Racemes digitately arranged (sometimes with a single raceme below the others). 26
24. Racemes inserted along the rachis. 25

25. Ligule absent, leaf sheath glabrous, annual. Echinochloa colona
25. Ligule a ring of hairs, leaf sheath hairy or at least with a ring of  hairs at the culm nodes, perennial. 27

26. Lower glume of spikelet 3-nerved. Urochloa mosambicensis
26. Lower glume of spikelet 7-nerved. Brachiaria brizantha

27. Spikelets awned. Chloris
27. Spikelets unawned. 28

28. Spikelets the shape of 1/2 of a sphere, flat on one side, rounded on the other, racemes 2-3 per culm. Paspalum scrobiculatum
28. Spikelets compressed about equally on both sides, with acute apices. 29

29. Spikelets hairy, at least on the veins. Digitaria
29. Spikelets glabrous. Cynodon dactylon

30. Spikelets awned, the awns > 5 mm long. Loudetia simplex
30. Spikelets unawned or with tiny awns to 3 mm long. 31

31. Fertile lemma of spikelet white and conspicuously transversely rugose, lemma and upper glume apices rounded to obtuse. Panicum maximum
31. Fertile lemma of spikelet not rugose, lemma and glume apices acute to very shortly awned. 32

32. Spikelets covered with long hairs nearly as long or longer than the spikelet. Melinus repens
32. Spikelets glabrous to pubescent but the hairs never more than 1 mm long, never obscuring the spikelet. Sporobolus

33. Inflorescence a panicle of racemes, inserted either digitately or racemosely. 34
33. Inflorescence an open panicle with individual spikelets terminating the branches. 37

34. Racemes digitate (sometimes with one inserted below the main group.) 35
34. Racemes inserted along the rachis. 36

35. Racemes rigidly at a right angle to the rachis and curving upward after releasing fruit. Dactylotenium
35. Racemes at obtuse angles to the rachis, not curving upward upon releasing fruit. Eleusine coracana

36. Lemmas shortly awned, paleas ciliate on the keels, spikelets laying along the raceme axis, racemes straight. Trichoneura grandiglumis
36. Lemmas acute but not awned, paleas not ciliate, spikelets hanging away from the raceme axis, racemes usually slightly curved upward. Pogonarthria squarrosa

37. At least the lower florets in each spikelet awned. 38
37. None of the florets awned. Eragrostis

38. Lower lemmas with at least one awn longer than the body of the lemma, lemmas copiously long hairy. 39
38. Lower lemmas with their awns shorter than the body of the lemma, lemmas very short pubescent to glabrous. Lintonia nutans

39. One or both of the glumes more than half the length of the entire spikelet (including awns), plants < 80 cm tall, lemmas with a single awn. Schmidtia ppophoroides
39. Niether of the glumes more than half the entire length of the spikelet (including awns), plants usually > 80 cm tall, lemmas with a prominent central awn and two inconspicuous lateral awns. Triraphis schinzii

40. Raceme pairs forming a >- with their common pedicel. Hyparrhenia
40. Raceme pairs forming a <- with their common pedicel. Cymbopogon caesius
 

THE SPECIES
 

Andropogon gayanus Kunth Blue Grass

Aristida L.

1. Spikelets > 50 mm long (including awns). Aristida stipitata
1. Spikelets < 50 mm long (including awns). 2

2. Articulation line between the lemma and the column made by the joined bases of the awns clearly visible, lower glume awned. 3
2. Articulation line between the lemma and the column made by the joined bases of the awns not clearly visible, lower glume awned or not. 5

3. Leaf auricles (at the top of the sheath). wooly pubescent. Aristida meridionalis
3. Leaf auricles glabrous. 4

4. Slender plants < 70 cm tall, spikelets > 20 mm long (including awns). Aristida congesta
4. Robust plants > 70 cm tall, spikelets mostly < 20 mm long, always < 26 mm long (including awns). Aristida pilgeri

5. Awn of lower glume > 0.8 mm, spikelets mostly one to a few on lateral branches at near right angles to the culm, the awns also at near right angles to the spikelet, spikelets 35-50 mm long (including awns). Aristida rhiniochloa
5. Awn of lower glume < 0.8 mm or absent, spikelets in a lax or compact panicle but not on single branches rigidly at near right angles to the culm, awns at clearly acute angles to the spikelet, spikelets 10-40 mm long. 6

6. Spikelets in an open, lax, often nodding panicle with the spikelets in clusters of no more than 2-3. Aristida effusa
6. Spikelets densely clustered into one or a few groups of many together. 7

7. Inflorescence a densely clustered, cylindrical panicle. Aristida condensata
7. Inflorescence of 2-5 dense clusters separated by bare panicle branches, usually a central one with 2-3 lateral ones below it. Aristida barbicolis

Aristida adscensionis L. Annual Bristle Grass, Annual Three-awn
Aristida barbicolis Trin. & Ruprec.Spreading Prickle Grass, Spreading Three-awn
Aristida congesta Roem. & Schult. Tassel Three-awn
Aristida effusa Henr. Spreading Steekgrass
Aristida meridionalis Henr. Giant Three-awn
Aristida pilgeri Henr. Pilger's Three-awn
Aristida rhiniochloa Hochst. Large-seeded Three-awn
Aristida stipitata Hack. Long-awned Three-awn
 

Bothriochloa Kuntze

1. Lemmas with a clear, tiny hole in the back, just above the center. Bothriochloa insculpta
1. Lemmas without a tiny hole in the back. Bothriochloa radicans

Bothriochloa insculpta (A.Rich.) A.Camus Pinhole Grass
Bothriochloa radicans (Lehm.) A. Camus Stinking Grass

Brachiaria brizantha (A.Rich.) Stapf Common Signal Grass

Cenchrus ciliaris L. Blue Buffalo Grass

Chloris Swartz

1. Lemma with an awn of at least 4 times the length of the lemma itself and an apical tuft of hairs at least 1/2 as long as the lemma itself and obscuring its apex. Chloris virgata
1. Lemma with an awn equal to or shrter than the length of the lemma itself and without its tip obscured by a tuft of hairs. Chloris gayana

Chloris gayana Kunth Rhodes Grass
Chloris virgata Swartz Feathered Chloris

Chrysopogon serrulatus Trin. Golden Beard Grass

Cynodon dactylon (L.) Pers. Couch Grass

Cymbopogon caesius (Hook. & Arn.) Stapf Turpentine Grass
 

Dactylotenium Willd.
 

1. Plants annual, robust, erect, racemes 3-9. Dactylotenium giganteum

1. Plants perennial, stoloniferous, racemes 1-3 (usually 2). Dactyloteniumaustrale
 

Dactylotenium australe Steud. Natal Crowfoot, Durban Grass, L.M. Grass

Dactylotenium giganteum Fisher and Schweick.  Giant Crowsfoot, Duck Grass

Dichanthium annulatum (Forssk.) Stapf
 

Digitaria Haller

1. Annual, without stolons or rhizomes. Digitaria sanguinalis
1. Perennials with stolons and rhizomes. 2

2. Base of culm bulbous and covered with densely hairy scales, lower lemma with purple to silvery hairs. Digitaria seriata
2. Base of culm not appreciably swollen or bulbous, not covered with densely hairy scales, lower lemma with yellowish to brown hairs. Digitaria milanjiana

Digitaria milanjiana (Rendle) Stapf Milanje Finger Gras
Digitaria sanguinalis (L.) Scop. Crab Finger Grass
Digitaria seriata Stapf Kuruman Finger Grass
 

Dinebra retroflexa (Vahl) Panz. Cat's Tail Vlei Grass

Echinochloa colona (L.) Link Jungle Rice

Eleusine coracana (L.) Gaertn. Goose Grass, African Finger Millet
 

Enteropogon Nees
 

1. Awn of lowest lemma in the spikelet 10-18 mm long. Enteropogon macrostachyus

1. Awn of lowest lemma in the spikelet 1-5 mm long. Enteropogon ruprestris

Enteropogon ruprestris ((J.A.Schmidt) A. Chev.
Enteropogon macrostachyus (A.Rich) Benth. Needle Grass
 

Eragrostis N.M. Wolf

1. Mature spikelets > 3 mm wide, disarticulating below the glumes. Eragrostis superba
1. Mature spikelets < 3 mm wide, disarticulating above the glumes. 2

2. Inflorescence with sticky glands (particles of dirt often stuck on them in patches), annuals. Eragrostis viscosa
2. Inflorescence without sticky glands, perennials. 3

3. Inflorescense with at least 3 orders of branching, open spreading, robust grasses, generally > 60 cm tall. 4
3. Inflorescence with 1-2 orders of branching, almost racemose, with only a few spikelets per primary branch, plants slender, generally < 50 cm tall. Eragrostis nindensis

4. Palea keels broad and flat, culms generally yellow, leaves mostly basal, not curling when dry. Eragrostis pallens
4. Palea keels a thin line, culms green to tan, leaves often cauline, often curling when dry. Eragrostis rigidior

Eragrostis nindensis Fical. & Hiern. Wether Love Grass
Eragrostis pallens Hack. Broom Love Grass
Eragrostis rigidior Pilg. Broad-leaved Curly Leaf
Eragrostis superba Peyr. Sawtooth Love Grass
Eragrostis viscosa (Retz.) Trin. Sticky Love Grass
 

Heteropogon contortus (L.) Roem. & Schult. Spear Grass

Hyparrhenia Fourn.

1. Spikelets covered with brown hairs, 9-14 awns per pair of racemes. Hyparrhenia rufa
1. Spikelets glabrous or with white hairs, 2 (sometimes to 4) awns per pair of racemes. Hyparrhenia filipendula

Hyparrhenia filipendula (Hochst.) Stapf Fine Thatching Grass
Hyparrhenia rufa (Nees) Stapf Giant Thatching Grass

Hyperthelia dissoluta (Steud.) Clayton Yellow Thatching Grass

Ischaemum afrum (J.F. Gmel) Dandy Turf Grass

Lintonia nutans Stapf

Loudetia simplex (Nees) C.E. Hubb. Common Russet Grass

Melinus repens (Willd.) C.E. Hubb. Natal Red Top

Panicum maximum Jacq. Guinea Grass, Buffalo Grass

Paspalum scrobiculatum L. Veld Paspalum

Pennisetum purpureum Schum. Napier Fodder, Elephant Grass

Perotis patens Gand. Bottlebrush Grass, Purple Spike Grass, Cat's Tail

Phragmites mauritianus Kunth. Spear Reed

Pogonarthria squarrosa (Roem. & Schult.) Pilg. Herringbone Grass

Rottboellia cochinchinensis (Lour.) Clayton Guineafowl Grass

Schizachyrium jeffreysii (Hack.) Stapf Silky Autumn Grass

Schmidtia pappophoroides Steud. Sand Quick
 

Setaria P. Beauv.

1. Inflorescence a compact spicate panicle, lower glume 1- nerved, plants annual. Setaria verticillata
1. Inflorescence a spike or spicate raceme, lower glume 3-nerved, plants perennial or annual. 2

2. Culm nodes glabrous. 3
2. Culm nodes hairy. 4

3. Plants annual, inflorescence < 5 times as long as wide, upper lemma coarsely rugose. Setaria ustilata
3. Plants perennial, inflorescence > 5 times as long as wide, upper lemma not coarsely rugose. Setaria sphacelata

4. Spikelets 2.5-3.0 (rarely to 3.7) mm long, basal plant parts tan. Setaria incrassata
4. Spikelets 3.5-5.0 mm long, basal plant parts dark colored. Setaria nigrirostis

Setaria incrassata (Hochst.) Hack. Vlei Bristle Grass
Setaria nigrirostis (Nees) Dur. & Schinz Black-seed Bristle Grass
Setaria sphacelata (Schum.) Moss Common Bristle Grass
Setaria ustilata De Wit Shade Bristle Grass
Setaria verticillata (L.) Beauv. Bur Bristle Grass

Sorghum Moench.

1. Culm nodes with a ring of spreading white hairs, mature fruit black. Sorghum versicolor
1. Culm nodes very short pubescent to glabrous, mature fruit yellow to tan. Sorghum bicolor

Sorghum bicolor (L.) Moench. Common Wild Sorghum
Sorghum versicolor Anderss. Black-seed Wild Sorghum

Sporobolus R.Br.

1. Caryopses ("seed") orange to bright red-brown and round at maturity, plants annual, inflorescence < 5 times as long as wide, open with the branches in a few whorls. Sporobolus panicoides
1. Caryopses light brown to black, ovate, plants perennial, inflorescence a compact to open panicle more than 5 times longer than wide, with its branches only weakly whorled at a few of the nodes. 2

2. Panicle narrow, spike-like, spikelets 2.0-2.8 mm long. Sporobolus africanus
2. Panicle not spike-like, spikelets 1.7-2.0 mm long. Sporobolus pyramidalis

Sporobolus africanus (Poir.) Robyns & Tourney Rat's Tail Dropseed
Sporobolus panicoides A. Rich. Famine Grass
Sporobolus pyramidalis Beauv. Cat's Tail Dropseed
 

Stipagrostis uniplumis (Licht.) DeWinter Silky Bushman Grass

Themeda triandra Forssk. Rooigras

Triraphis schinzii Hack.

Trichoneura grandiglumis (Nees) Ekman Rolling Grass

Urochloa mosambicensis (Hack.) Dandy Bushveld Signal Grass