Southern African species of Mentha L. (Lamiaceae)

The species of Mentha L. occurring in Southern Africa are reviewed and a key is provided to two indigenous and one naturalized species. M. wissii Launert is reduced to M. longifolia (L.) Huds. subsp. wissii (Launert) Codd. Although Mentha is a clearly defined genus, the determination of species limits is not an easy matter and there has been a proliferation of ‘species’ by certain authors in Europe. The result is that over a thousand specific and infraspecific names have been published, while conservative estimates place the number of good species at between twenty and thirty, most of which occur in the northern hemisphere. Perhaps Walahfrid Strabo was justified when, in the ninth century A .D ., he included the following lines in his ‘Hortulus’ (reproduced, with translation, by the Hunt Botanical Library, 1966): ‘But if any man can name The full list of all the kinds and all the properties Of mint, he must be one who knows how many fish Swim in the Indian Ocean, how many sparks Vulcan Sees fly in the air from the vast furnace in Etna’. Part of the difficulty in deciding on species limits has been attributed to hybridization. It is also evident that some species are extremely polymor­ phic, particularly M. longifolia (L.) Huds., in which 21 subspecies and 150 varieties were recognized by Briquet. The nomenclature of this species and of the related M. spicata L. has also been complicated by Linnaeus adopting a different treatment of the complex in the second edition of his Species Plantarum (1763) from that of the 1753 edition. In his first edition of 1753, Linnaeus treated members of this complex as three varieties within a single species without indicating a typical variety, as follows: M. spicata L. a. var. viridis L. b. var. longifolia L. c. var. rotundifolia L. In edn 2 (1763), he raised the three varieties to species rank, but discarded the name M. spicata: 1. M. viridis (var. viridis L., edn 1) 2. M. sylvestris (var. longifolia L., edn 1) 3. M. rotundifolia (var. rotundifolia L., edn 1). However, in the meantime, Hudson in his Flora Anglica (1762) had dealt with them on the following lines which conform with the modern approach: 1. M. spicata (var. viridis L., edn 1) 2. M. longifolia (L.) Huds. 3. M. rotundifolia (L.) Huds. Unfortunately, most subsequent authors, until recently, have followed the nomenclature put ’ Botanical Research Institute, Department of Agriculture, Private Bag X101, Pretoria 0001, South Africa. forward in Linnaeus’s second edition instead of Hudson’s earlier and more logical treatment which should have been adopted. In the latter part of the same century, J. E. Smith, who had distinguished himself in 1784 by acquiring the Linnaean Herbarium, made a study of British mints and published his conclusions in Trans. Linn. Soc. London 5: 171-217 (1899). One point which affects our flora was his clarification of the distinction between M. longifolia and M. spicata on the basis of the retrorse-pubescent rhachis and the densely pubescent pedicels and calyx of M. longifolia as against the glabrous to sparingly pubescent parts of M. spicata. Although this may serve as a basis for distinguishing between the two species, exceptions may be encountered (Harley 1972, 1972a; Harley & Brighton 1977). Over the greater part of its distribution range in southern Africa, M. longifolia (in which three subspecies are recognized) exhibits the characteristically pubescent rhachis and calyx. However, in a small area in the southern Cape Province between Humansdorp and Riversdale, and inland to the Swartberg, specimens have been recorded in which all parts are glabrous but which in general appearance agree with M. longifolia rather than with M. spicata. The link with M. longifolia is further supported by the occurrence of specimens with intermediate grades of pubescence. Cooke in Flora Capensis identified such glabrous specimens (Burchell 4798, 6457) as M. viridis (a synonym of M. spicata) but, with more ample material now available, it is considered that they belong in M. longifolia as a form of subsp. polyadena and that Cooke’s key to the species and subspecies should be modified accordingly. In the present study it is concluded that M. spicata does not occur naturally in southern Africa, though it has been found as a recent adventive. It is therefore unlikely that the glabrous and intermediate specimens referred to above have been derived from hybridization between M. longifolia and M. spicata. Several species are grown for their essential oils or as culinary herbs, the best known being the Peppermint (A/, x piperita L.) and the Spearmint (M. spicata,), both of which have been tried commercially in South Africa and are discussed by Baarschers, Horn & Rehm (1962). Several species are used medicinally, as is the case with the two indigenous species, M. longifolia and M. aquatica. The common mint, M. spicata, is widely grown for mint sauce and has been found as a garden escape here and there. 170 SOUTHERN AFRICAN SPECIES OF MENTHA L. (LAM IACEAE) KEY TO SPECIES A N D SUBSPECIES IN SOUTHERN AFRICA. Leaves sessile or subsessile; inflorescence cylindrical, tapering, 10-14 mm in diameter: Rhachis, pedicels and calyx pubescent: Leaves linear, 2 4 mm broad.............................................................................................la. M. longifolia subsp. wissii Leaves linear-lanceolate to lanceolate or oblong-lanceolate, more than 5 mm broad: Leaves variously pubescent on one or both surfaces..........................................lb. M. longifolia subsp. capensis Leaves glabrous or with a few scattered hairs beneath.................................... lc. M. longifolia subsp. polyadena Rhachis, pedicels and calyx glabrous, though calyx teeth may be ciliate: Leaves lanceolate, acuminate, margins shortly and often obscurely toothed, lc. M. longifolia subsp. polyadena Leaves oblong to ovate-elliptic, acute to obtuse, margin serrate; calyx teeth often c iliate................2. M. spicata Leaves usually petiolate; inflorescence of oblong or globose flower clusters, 14-20 mm in diameter..3. M. aquatica 1. Mentha longifolia (L.) Huds., FI. Angl. ed. 1: 221 (1762); Briq. in Naturl. Pfl.Fam. 4,3a: 321 (1896). Cooke in FI. Cap. 5,1: 304 (1910). Type: from Europe. M. spicata var. longifolia L., Sp. PI. 576 (1753). M. sylvestris L., Sp. PI. ed. 2,2: 804 (1763); Smith in Trans. Linn. Soc. Lond. 5: 179 (1800); Bak. in FI. Trop. Afr. 5: 451 (1900). nom. illegit.

forward in Linnaeus's second edition instead of Hudson's earlier and more logical treatm ent which should have been adopted.
In the latter part of the same century, J. E. Smith, who had distinguished himself in 1784 by acquiring the Linnaean Herbarium, made a study of British mints and published his conclusions in Trans.Linn.Soc.London 5: 171-217 (1899).One point which affects our flora was his clarification of the distinction between M. longifolia and M. spicata on the basis of the retrorse-pubescent rhachis and the densely pubescent pedicels and calyx of M. longifolia as against the glabrous to sparingly pubescent parts of M. spicata.
Although this may serve as a basis for distinguishing between the two species, exceptions may be encountered (Harley 1972(Harley , 1972a;;Harley & Brighton 1977).Over the greater part of its distribution range in southern Africa, M. longifolia (in which three subspecies are recognized) exhibits the characteristically pubescent rhachis and calyx.However, in a small area in the southern Cape Province between Humansdorp and Riversdale, and inland to the Swartberg, specimens have been recorded in which all parts are glabrous but which in general appearance agree with M. longifolia rather than with M. spicata.The link with M. longifolia is further supported by the occurrence of specimens with intermediate grades of pubescence.Cooke in Flora Capensis identified such glabrous specimens (Burchell 4798, 6457) as M. viridis (a synonym of M. spicata) but, with more ample material now available, it is considered that they belong in M. longifolia as a form of subsp.polyadena and that Cooke's key to the species and subspecies should be modified accordingly.In the present study it is concluded that M. spicata does not occur naturally in southern Africa, though it has been found as a recent adventive.It is therefore unlikely that the glabrous and intermediate specimens referred to above have been derived from hybridization between M. longifolia and M. spicata.
Several species are grown for their essential oils or as culinary herbs, the best known being the Peppermint (A/, x piperita L.) and the Spearmint (M.spicata,), both of which have been tried commercially in South Africa and are discussed by Baarschers, Horn & Rehm (1962).Several species are used medicinally, as is the case with the two indigenous species, M. longifolia and M. aquatica.The common mint, M. spicata, is widely grown for mint sauce and has been found as a garden escape here and there.Perennial rhizomatous herb; stems erect to straggling, up to 1,5 ( -2 ) m long, usually retrorse-tomentose, rarely (southern Cape) glabrous or subglabrous.Leaves sessile to shortly petiolate; in southern Africa linear to linear-lanceolate, lanceo late or lanceolate-oblong, glabrous to finely felted or coarsely pubescent or white-tomentose beneath (see subspecies), freely gland-dotted, apex acuminate, base obtuse to truncate, margin entire to shortly and distantly toothed.Inflorescence cylindrical, tapering at the apex, 30-100 x 10-12 (-1 4 ) mm, usually of many verticils, often somewhat lax below, dense above; rhachis usually densely retrorse-tomentose, rarely subglabrous or glabrous; bracts reduced, bracteoles linear; pedicels usually hispid.Calyx tubular-campanulate, 2 -2 ,5 mm long, densely to sparingly glandular hispid, rarely glabrous (southern Cape).Corolla white to mauve, 3 -5 mm long.Stamens exserted or occasionally abortive.
An extremely polymorphic species, widespread in Europe and the Mediterranean region to eastern Asia, the Canary Islands and extending to Ethiopia and Kenya from where there is a gap to Zimbabwe and southern Africa, where 3 subspecies are recognized (see Key).Known in England as Horse Mint because the leaves are usually unpleasantly scented.
If the South African material were studied in isolation it is probable that separate species status would be accorded to subsp.capensis and subsp.polyadena, with subsp.wissii placed as a subspecies of M. capensis.Although subsp.capensis and subsp.polyadena overlap in Lesotho and in parts of the southern Cape, there are few specimens which can be regarded as intermediate between them.How ever, seen in perspective, they are obviously extensions of the M. longifolia complex.In the northern hemisphere the leaves of this species may be ovate to ovate-oblong or oblong-lanceolate, but in southern Africa the leaves tend to be narrower in relation to the length, being lanceolate-oblong to linear-lanceolate or linear (subsp.wissii).In this region, subsp.polyadena, with glabrous leaves, is probably one of the most clear-cut subdivisions of the species.In subsp.capensis the leaves vary a good deal in the degree of pubescence and the subject is discussed more fully under the subspecies.For obvious reasons synonymy has been limited to names applicable in southern Africa.

Mentha wissii
Recorded from two localities in South West Africa/Namibia (the Brandberg and Naukluft) and from near Garies in Namaqualand; in watercourses and moist places.The leaves are said to be strongly and unpleasantly aromatic.This group of specimens is very closely allied to subsp.capensis and is separated only on the grounds of the rather distinctive linear leaves.The pubescen ce of the leaves and the inflorescence characters are in no way different from subsp.capensis.One or two specimens from N am aqualand have linearlanceolate leaves and are therefore intermediate between subsp.wissii and subsp.capensis.In addition, Dr Harley (personal communication) has informed me that, in cultivation, subsp.wissii sometimes produces broader leaves than usual, suggesting that separate status for subsp.wissii can scarcely be supported.However, the plants from the wild state with linear leaves can be recognized without difficulty and, because they occupy a separate geographical area, it is considered that subspecies status is appropriate in the present state of our knowledge.Leaves sparingly to finely pubescent and greyish to dark coloured above, densely white-tomentose to thinly greyish pubescent beneath, lanceolate to linear-lanceolate, (3 0 -) 4 5 -9 0 (-1 0 0 ) x ( 5 -) 7 -1 8 (-2 2 ) mm. apex acuminate, base obtuse to truncate, margin entire to shortly and distantly toothed.(Fig. la, b, c.)A fair amount of variation in leaf pubescence is included in the above concept of subsp.capensis.Subsp.capensis appears to be absent from an area in the southern Cape between Humansdorp and Riversdale and, inland, to the Swartberg, in which area it is replaced by a form of subsp.polyadena.Along the margins of this area there appears to be some introgression between the two subspecies.Examples of specimens which have dark green concolorous leaves like subsp.polyadena but with the leaf surface puberulous to sparingly pubescent, especially on the nerves beneath are: Lewis 4222 and Barker 7883 from the Humansdorp area, and Burchell 7196 from near Riversdale.These speci mens are all included in subsp.polyadena but an intermediate specimen with more strongly develo ped pubescence, Goldblatt 1686 from near Montagu, is included in subsp.capensis.On the other hand, both subspecies occur in Lesotho with no evidence of intermediates occurring.Commonly known in the Karoo and Namaqua land as Balderjan or variations of it, such as Ballerja, Balterja etc.It is also referred to as Wild Mint or Kruisement (Kruistemunt) from the Dutch name for M. spicata.The leaves are variously described as having a strong mint-like odour or as smelling of peppermint and are frequently used as a tea to relieve colds and fevers.For this purpose the leaves may be boiled with a little water and sugar until a syrup is formed, of which a tablespoonful is taken three times a day (Hanekom 1378).
In Lesotho the vernacular name for both subsp.capensis and subsp.polyadena is 'koena', a crocodile, reputedly because the plants occur in wet places.Another reason could be that the lanceolate, tapering leaves with small teeth are reminiscent of the shape of the reptile as seen from above.In addition to an infusion being taken as a cure for colds, fresh plants are put under the bedding of a patient in the belief that this will help him to breathe more easily.Leaves glabrous on both surfaces or with a few scattered hairs, lanceolate to elliptic-lanceolate or oblong-lanceolate, 35-80 x 8 -1 8 mm, apex acuminate, base obtuse to truncate, margin usually shortly toothed, occasionally subentire.Rhachis usually retrorse-tom entose, occasionally glabrous -see note below.(Fig. 2.) Recorded from two disjunct areas: (a) from the Transvaal, Swaziland, northern Natal, eastern Orange Free State and northern Lesotho; and (b) from the southern Cape Province between the Humansdorp and Riversdale districts and inland to the Swartberg (Fig. 5).Found along watercourses, on river banks and in moist places.The specimens from area (a) are relatively uniform with the rhachis retrorse-tomentose and the calyx densely glandular-pubescent.In area (b), on the other hand, there is a good deal of variation in the degree of pubescence of the rhachis.Some specimens are typical (Oliver 5661), some are sparsely pubescent (Muir 1973(Muir , 2004, Dahlstrand 3506), whereas others are completely glabrous {Acocks 18189, Fourcade 3235).In all the specimens from area (b) the leaf shape is lanceolate to oblong-lanceolate, acuminate, and the general appearance is so similar to the rest of the complex that it would be illogical to separate the glabrous specimens from subsp.polyadena, as was done by Cooke in Flora Capensis.
In M. spicata (= A/, viridis), the rhachis and calyx are glabrous but the South African records of this species, which are considered to be garden escapes, have ovate-oblong leaves with serrate margins and can usually be readily distinguished from the glabrous specimens of M. longifolia subsp.polyade na.
It is interesting that subsp.capensis, which is common in the rest of the Cape Province, appears to be absent from area (b).The two subspecies meet in the Humansdorp, Riversdale, Montagu and Swart berg areas and the evidence of introgression between the two is discussed under subsp.capensis.As noted previously, the two occur together in Lesotho, but no intermediates from this area have been encountered.The qualifying notes relating to pubescence after the Cape specimens refer to the pubescence of the rhachis and calyx.
The plant is used medicinally in the same way as subsp.capensis.

2.
Mentha Perennial rhizomatous herb; stems ascending up to 600 mm tall, glabrous to sparingly pubescent.Leaves sessile to shortly petiolate; blade glabrous or nearly so, somewhat rugose, freely gland-dotted on both surfaces, lanceolate-oblong to ovate-oblong or ovate, 30-50 (-6 0 ) x 13-20 mm, apex acute, base obtuse to truncate, margin serrate.Inflorescence cylindrical, 30-60 x 10-14 mm; rhachis and pedicels glabrous; bracts reduced, bracteoles linear, glabrous.Calyx tubular-campanulate, 2 -2 ,5 mm long, glabrous; teeth sometimes ciliate.Corolla mauve to whitish, 4 mm long.(Fig. 3.) Commonly known as Spearmint, this is the most widely grown species in kitchen gardens for mint sauce etc, and is also cultivated commercially for its essential oil, which is used medicinally and in confectionery.Its origin is lost in antiquity, having probably arisen in cultivation in Europe in ancient times.Its chromosome complement (usually 2n = 48) suggests that it is an allopolyploid, possibly derived from M. suaveolens Ehrh.and M. longifolia (L) Huds., both of which normally have 2n = 24 (Harley, I.e.).It exists in a wide range of forms, the more desirable ones being propagated vegetatively, and the species is now widely naturalized throughout the world.In South Africa it has been recorded as a garden escape here and there, in moist places.As pointed out under the previous heading, certain Burchell specimens identified as M. viridis by Bentham in DC., Prodr.12: 168 (1848) and Cooke in FI.Cap.5,1: 305 (1910) are now considered to be a glabrous form of M. longifolia subsp.polyadena.
Widely distributed in Europe and around the Mediterranean, extending eastwards to Siberia; found in tropical Africa from Kenya, Tanzania, Zaire and Malawi, with a record from the swamps of northern Botswana; locally common in marshes and wet places in the higher rainfall areas of the Transvaal and adjacent parts of northern Cape and Swaziland, widespread in Natal, eastern O.F.S. and Lesotho, extending through eastern Cape, along the coast to the Peninsula and northwards along the mountains to Ceres.(Fig. 6.) F ig .6 .-•, Mentha aquatica.
There is a good deal of variation in leaf shape from lanceolate to broadly ovate, and in pubescence from glabrous (Louw 1391 and Leendertz sub TRV11519 from western Transvaal) to a densely tomentose condition (Galpin 14807, 14830, Breijer sub TRV16991 and Mauve 4860 from Natal).However, there is a complete range of intermediate forms and no clear geographical pattern in the variation emerges.The leaves are usually petiolate but may be subsessile in some specimens.The latter may be readily separated from M. longifolia and M. spicata by the often widely spaced, oblong to globose flower clusters with the lower clusters, when present, being subtended by normal leaves.
M. aquatica is said to have a strong minty scent and is known as W ater Mint or Kruisement (Kruistement).An infusion of the leaves is taken for colds and as a tonic, being highly regarded (Hanekom 1379) as a treatment for promoting the flow of milk in nursing mothers.

F
ig .5 .-■, Mentha longifolia su b sp .wissii; A .M. longifolia s u b sp .capensis; o , M. longifolia su b sp .polyadena (ty p ic a l); • , M. longifolia s u b sp .polyadena (g la b r o u s r h a c h is); » , M. longifolia su b sp .polyadena (sp a r in g ly p u b e sc e n t r h a c h is).

Launert in Mitt. bot. StSamml., Miinch. 2: 311 (1957); Launert & Schreiber in Prodr. FI. S.W. Afr. 123: 19 (1969). Tvpe: S.W .A./Nam ibia, Brandberg. Wiss 1418 (FR. holo.; M; PRE!).
The typical form, with leaves white-tomentose beneath and greyish to dark-coloured above, includes the types of M. salicina Burch, ex Benth., subsp.obscuriceps Briq., subsp.doratophylla Briq., var.latifolia Benth.and var.cooperi Briq.ex Cooke.This form is distributed from the Orange Free State and adjacent parts of the south-western Transvaal, northern Cape and Lesotho to the eastern Cape and to the Peninsula, extending northwards to the Calvinia District.Specimens are now included in subsp.capensis from north of this distribution area, e.g. from western Transvaal ( Thode A1488, Leendertz sub TRV 11518), northern South West Africa/Namibia (Leistner et al. 143) and from Zimbabwe, which have concolorous grey-green leaves, finely pube scent above and thinly to coarsely pubescent beneath.Specimens with leaves having similar pubescence are found sporadically further south, e.g.Pearson 1553 and Compton 8512 from the Laingsburg area, and Pappe s.n.from Devils Peak.A specimen with pubescence of this kind ( Ecklon & Zeyher 673 from Uitenhage area) was described as subsp.bouvieri Briq.In fact, further study is desirable of the extent to which the present concept of subsp.capensis grades into M. longifolia subsp.schimperi (Briq.)Briq. of Ethiopia and other forms of M. longifolia from the northern hemisphere.