Aloe microstigma

Aloe microstigma was described and illustrated by Prince Salm-Reifferscheid-Dyck (1854: § 26 f. 4). It is the most widespread of the aloes in the section and has a disjunct distribution: it is widespread in the western parts of the Eastern Cape, the central areas of the Western Cape, and just into the Northern Cape in the Tankwa Karoo, and disjunctly in the far Northern Cape just south of the Orange River, South Africa, as well as in southwestern Namibia. It grows on rocky outcrops, sometimes on steep slopes, in karroid, desert, semidesert, and Namaqua Broken Veld vegetation (Klopper 2014).

Aloe microstigma is closely related to A. khamiesensis from western South Africa (Van Wyk & Smith 1996, 2014) and A. gariepensis from the Orange River Valley in the Northern Cape, South Africa, and southern Namibia (Glen & Hardy 2000, Carter et al. 2011). Aloe khamiesensis is in fact treated as conspecific with A. microstigma by certain authors (e.g., Glen & Hardy 2000), while plants attributed to the eastern form of A. gariepensis (between Keimoes, Northern Cape, South Africa, and Warmbad, Namibia) are considered by some to be a possible variant of A. microstigma (e.g., Carter et al. 2011). Aloe pictifolia a cliff-dweller from the Eastern Cape, South Africa, is also at times considered to be a close ally (Carter et al. 2011).

Aloe brunnthaleri A.Berger ex Cammerloher (1933: 131) is regarded to be a yellow-flowering form of A. microstigma (Reynolds 1950). Aloe brunnthaleri was used as a provisional name by Alwin Berger for a plant collected in the early 1900s by Joseph Brunnthaler near Matjiesfontein in the Western Cape, South Africa. The name appeared in a catalogue, Collection des Plantes Grasses du Jardin Botanique de Monaco, in 1921. It was, however, never formally published by Berger and thus remained a nomen nudum, until Herman Cammerloher validated the name based on the description of a plant that flowered in the botanical garden of the University of Vienna in January of 1930 and 1933 (Cammerloher 1933). This yellow-flowered form is known from several localities north of the Swartberg in the Western Cape (e.g., at Matjiesfontein, Laingsburg, and Beaufort West) and the Northern Cape (e.g., at Sutherland and Fraserburg), South Africa, and more recently also reported from the Gannaga Pass in the Tankwa Karoo National Park, Northern Cape, South Africa (Bester et al. 2012).

Namibian plants currently assigned to A. microstigma were previously described as A. juttae Dinter (1923: 159), but for a long time this name has been treated as a synonym of A. microstigma (Reynolds 1950). Because of morphological differences between A. juttae and A. microstigma, as well as the outlier distribution range of the Namibian plants, certain people feel strongly that these Namibian plants should be recognised at specific or subspecific level (J.J. Lavranos, pers. comm.). Indeed, the disjunction in the distribution ranges of these populations of A. microstigma has long been a source of uncertainty (Kemble 2011). Suggestions have even been made that the Namibian populations of A. microstigma might have closer affinities to A. framesii, because of their geographical proximity and the fact that both entities often form large groups (according to W.J. Jankowitz and B. Kemble, pers. comms.).

However, the gap in the distribution has recently been reduced: plants believed to be A. microstigma were recently found on the Hunsberg (Namibia), in the Richtersveld, and on several inselbergs in Bushmanland, Northern Cape, South Africa (Kemble 2011; E.J. van Jaarsveld and P. Desmet, pers. comms.). Plants resembling A. microstigma occur on several inselbergs in the Bushmanland region of the far Northern Cape, South Africa; these include Achab, Aggeneys, Gamsberg, Namies, Witberg (P. Desmet, pers. comm.), and the Slangberg (J.C. Kruger, pers. comm.). Plants are confined to the crests of south-facing aspects and occur as scattered individuals and do not form discrete populations (P. Desmet, pers. comm.). These plants apparently do not differ from A. microstigma in any significant way, although they do form clumps (J.J. Lavranos, pers. comm.), suggesting a close affinity with the Namibian form (i.e., A. juttae). In some localities plants occur as solitary rosettes, and are believed to mix with A. gariepensis that is present on the north facing slopes of these inselbergs (P. Desmet, pers. comm.).

Williamson (2000) reported the occurrence of A. microstigma in the Richtersveld, Northern Cape, South Africa, stating that ‘the aloe is restricted to high ridges along the summit of the Stinkfonteinberge and the high eastern mountains overlooking the Orange River’. This aloe is not common in the Richtersveld and only two colonies are known from this region: one on the eastern aspect towards the summit of Cornellsberg, where plants grow on fairly rocky terrain of the Stinkfontein Subgroup amongst Richtersveld montane vegetation; and the second about halfway down the Klein Hellskloof, where plants grow among rocks of the Richtersveld Suite (G. Williamson, pers. comm.). There are also two known populations in the Sperrgebiet of southwestern Namibia: in a population towards the summit of the Heiob Mountain, plants grow on the eastern aspect; the population from the Rooiberg, just east of the Aurusberge, grows on the southern aspect (G. Williamson, pers. comm.). Plants resembling A. microstigma were also recently found at the eastern end of the Hunsberg in southern Namibia (E.J. van Jaarsveld, pers. comm.).

A specimen at Herb. NBG (A. Jooste 46, collected 7 August 1993) from the Akkerendam Nature Reserve just north of Calvinia in the Northern Cape, South Africa, was identified as ‘ Aloe cf. khamiesensis (description inadequate)’. However, this locality is outside the generally accepted distribution range of this aloe (even though aberrant forms of A. khamiesensis have been reported from near Calvinia). The Akkerendam Nature Reserve was visited in July 2010 to search for this population. Despite the NBG specimen label information describing the occurrence as ‘locally common’, only one plant was found, with the remains of a second dead plant close-by. No fruit were formed in the 2010 season, suggesting isolation from other plants (aloes are generally self-incompatible). Although the NBG specimen label indicates that no fruit were present, there are three capsules on one of the inflorescences that form part of this specimen, which suggests that the second plant was probably still alive and also flowering in 1993. The plant grows on a low rocky ridge on the plain (not on the footslopes of the Hantamsberg) in dwarf karroid shrubland. It is geographically relatively close to populations related to A. khamiesensis near Loeriesfontein to the northwest and populations of A. microstigma on the Bloukrans Pass just south of Calvinia. Morphologically the Akkerendam (Calvinia) plants more closely resemble A. microstigma and not A. khamiesensis, as was suggested by the determination on the NBG specimen.

Similar plants occur elsewhere in the Calvinia area, where huge numbers of plants are dying in some of the populations (F. van der Merwe, pers. comm.). Reasons for the mass die off could possibly be attributed to damage caused by aloe snout beetle activity, but more likely due to herbivory by porcupines (A.J. Urban, pers. comm.).

Plants in full flower resembling either A. framesii or A. microstigma were found near Kagga Kamma Nature Reserve in the Swartruggens Mountains (Cederberg region) in the Western Cape, South Africa, in early August 2012 (M. Koekemoer, pers. comm.).

It has been suggested by Mottram (2013) that the correct name for A. microstigma is A. perfoliata Linnaeus (1753: 319). According to the Index Nominum Genericorum (Farr & Zijlstra 1996 +), the latter name was also designated as the type of the genus name Aloe by Britton & Millspaugh (1920). Given the confused history and uncertainty of the application of the name A. perfoliata, the proposal of Mottram (2013) should perhaps be treated with circumspection. Aloe perfoliata has been recorded as an imperfectly known taxon by Reynolds (1950), even though there is a supposed type specimen annotated by Linneaus. Reynolds (1950) specifically referred to the Linneaus specimen (LINN 442.1) as ‘type’ material, thus effectively designating it as the lectotype of the name A. perfoliata (Art. 7.11, Turland et al. 2018). Glen & Hardy (2000) applied this name to a broad concept in which they included material today treated as (at least) three species, namely A. mitriformis Miller (1768: ALO, nr. 1), A. comptonii Reynolds (1950: 382), and A. distans Haworth (1812: 78), without a clear explanation for the reason behind this decision and superfluously lectotypified the name with plate 17 of Dillenius in Hortus Elthamensis 1: 21, t.17, fig.19 (1732). Mottram (2013) erroneously regarded another Dillenius plate in Hortus Elthamensis 1: 18–19, t.15, fig.16 (1732) as the lectotype for A. perfoliata. This view is based on citation of plate 15 by Scopoli (1783). However, since Scopoli (1783) did not specifically refer to the illustration as ‘type’ or an equivalent term, this is not a valid lectotypification (Art. 7.11, Turland et al. 2018) (for more details see Klopper et al. 2016). According to his interpretation of the lectotype of the name A. perfoliata, Mottram (2013) attempted to illustrate that plate 15 of Dillenius (1732) represents what we now call A. microstigma. The arguments provided by Mottram (2013) are not entirely convincing and the name A. microstigma is preferred for the purposes of this present study, until further clarity on the taxonomic identity of A. perfoliata can be obtained.