The identity of Eriosema nanum

An examination of available evidence leads to the conclusion that Eriosema nanum Burtt Davy must be regarded as a synonym of E. ellipticifolium Schinz. The relationship between E. ellipticifolium and E. uniflorum Burtt Davy is discussed.


INTRODUCTION
Eriosema nanum Burtt Davy, together with E. populifolium Harv.and E. angustifolium Harv., are among the rarest of the Fabaceae in South Africa.Recent intensive field studies of Eriosema (Stirton, 1975) showed the widespread occurrence of hybridi zation and of morphological variation in the genus in South Africa.This paper assesses various aspects of phenotypic plasticity and interspecific hybridi zation as they affect the identity and delimitation of E. nanum.HISTORY Schinz, in Vjschr. Naturf. Ges. Zurich 66: 229, 1921, based E. ellipticifolium on Junod 1411 from Shilouvane and Junod 2534 (Fig. 1) from Marovunge, both in the Eastern Transvaal.Owing to the absence of ripe or almost ripe fruits, he was unable to establish clearly whether he was dealing with a Rhynchosia or an Eriosema species ("Solange keine reifen oder nahezu reifen Friichte vorliegen, ist es vorlaufig ein aussichtsloses Bemiihen, feststellen zu wollen, ob es sich um eine Rhynchosia-oder eine Eriosema-Art handelt, sicher ist, dass sie sich mit keiner der mir bekannten Arten dieser oder jener Gattung deckt").He commented, however, that the plant was reminiscent of E. salignum, but differed in its lower surface indumentum.The name E. ellipticifolium has never been taken up.
In 1932 Burtt Davy treated E. ellipticifolium very briefly under the heading "species not seen".In this work, however, he published Eriosema nanum based on Galpin 1139 from the^summit of the Saddleback Mountain in the Barberton area (Fig. 2).As its allies he noted E. rufescens Schinz and E. burkei Benth.and commented also that it was perhaps closest to E. uniflorum Burtt Davy.A study of type specimens leaves no doubt that E. nanum is synonymous with E. ellipticifolium.Population studies showed that the wide leaf variation encountered is the result of a cline of decreasing width in a northerly direction (Stirton, 1975).The type localities of E. ellipticifolium occur in the northern extremities of this range.It is unfortunate that the more descriptive name nanum must be superseded.

FIELD OBSERVATIONS
Plants growing in full sun tended to be shorter and more compact than plants of the same species found growing under different intensities of shade.In Fig. 3 plants of E. ellipticifolium that were found growing in short open grassland (plant 1) are con trasted with those growing along a road bank in a pine forest (plant 2).Plant 1 can be seen to be smaller and more compact than plant 2. Other obvious differences, not all observable from the photographs, are the longer inflorescences, the thinner leaves and the less prominent secondary and tertiary venation in plant 2. Plants that grew through a thick canopy of grass had the same facies as the plants that grew in or along forest margins.These features can be clearly seen on Stir ton 1431.These various expressions of morphological form could possibly be the result of a competition balance of mineral nutrients, degree of light intensity, extent of water availability, or a combination of these and other factors.The plants shown in Fig. 3 were chosen as representative of the range of variation within the species after a critical inspection of their populations.

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V *»* Plants that grew in burnt veld (Fig. 3: 3) had a more stunted form than plants of the same species which grew in adjacent unburnt veld (Fig. 3: 4).These plants were collected on the same day.The various populations were observed subsequently and it was found that once the new grass had come away the "dwarf plants" began to grow lank so that by the end of the season they were similar, but still shorter, than plants collected in the adjacent tall unburnt grassveld.The plants that grew in the burnt veld had almost completed their flowering period by the time the plants which grew in the unburnt veld had begun to flower.
The observations in open veld and in forest, and in burnt and unburnt veld, were found to be consistent throughout the range of distribution of E. elliptici folium.The results lead me to suspect that once the type specimen of E. uniflorum Burtt Davy is compared, it will probably have a facies similar to plant 2 in Fig. 3 and hence synonymous with E. ellipticifolium.Compton (1974, pers. comm.) has indicated that he intends to incorporate E. uniflorum under E. nanum in his revised Flora of Swaziland.Judgement is here reserved until the type is traced, since the description of E. uniflorum has features linking E. ellipticifolium and Stirton 1482 (E. sp. nov.) allied to E. cor datum.On the Galpin 1139 sheet from the Bolus Herbarium there is a specimen Bolus 11854 that has three Bolus manuscript names; uniflorum,pumilum and cryptantha.Appended to the specimen is a note, apparently in N. E. Brown's handwriting, that says "We afterwards decided that this was probably a stunted form of E. burkei".The specimen is E. ellipticifolium.Field studies (Stirton, 1975), however, indicated that stunted forms of E. pauciflorum Klotzsch, rather than E. burkei, are deceptively similar to E. ellipticifolium.
The most noticeable variation observed in the field was the range in number of flowers per inflorescence.Plants of the same population were found to have inflorescences bearing from one to ten flowers.
Although most specimens have been reasonably easy to place in this species there remain a few problems.Hybridization cannot be ruled out as the cause of some complexing difficulties encountered in a recent field trip.Two populations in particular require a detailed study as in both areas E. elliptici folium grows sympatrically with the rare E. angustifolium Burtt Davy and an undescribed taxon.A feature of these populations is their marked geographical separation viz.Magoebaskloof (N.Transvaal) and Havelock (Swaziland) and also the wide range of "intermedates" found.Flower colour, pubescence and the shape of stipules have been shown in preliminary hybridization studies (Stirton, 1975) on other species to be reliable indicators of putative hybrids.These three characters varied markedly in "intermediate" plants in both popu lations.E. angustifolium has a striking, stiff, rufous, patent indumentum, linear leaves, erect habit, and yellow flowers, and is not readily confused with either E. ellipticifolium or Stirton 1445 (E.sp.)The latter occurs from the N. Transvaal southwards to Swaziland and although fairly common in isolated areas has not been previously collected.This multi stemmed plant is a pink and yellow flowered perennial with prostrate habit, and small unifoliolate leaves.Its closest affinity is E. ellipticifolium.The intermediate plants at Magoebaskloof seem to be hybrids between E. angustifolium and E. ellipticifolium (Stirton 1442), and between Stirton 1445 (£.sp.) and E. ellipticifolium (Stirton 1446).Further field studies are necessary before all three putative parents are clearly delimited.The inter-relationships of these three species remain obscure.
Three specimens named E. ellipticifolium in this study are doubtful: these are Jacobsen 1587, Coetzer 150, and Vahrmeijer 2433.The last two of these, although very close to E. ellipticifolium, differ in pubescence and their very acute leaves.All these will no doubt be easier to place once all the montane species of Eriosema have been studied.

Eriosema ellipticifolium
Eriosema ellipticifolium is restricted to isolated mountain "islands" in Swaziland, the Transvaal and Natal (Fig. 5).This species exhibits a disjunct distri bution over a wide area and over diverging ecological conditions and veld types.If is found between 1 600-2 500 m growing predominantly amongst rocks in short grassland on dry ridges with a northwest aspect.A number of populations has been located on forest margins and along forest roads at the Witklip, Mariepskop and Woodbush Forest Reserves.Junod 2534 is chosen as lectotype, since the quantitative data given in the protologue indicates that Schinz must have based most of his description on the two specimens on this sheet.
This little-known species has proved to be more common and widespread than was previously accepted.The available herbarium material had been placed under no less than six species.It had been most commonly confused with Eriosema cordatum var.cordatum, but is readily separated from this and all other species by its very long calyx lobes which almost equal the length of the flower.
Despite its widespread distribution (Fig. 5) this species is remarkably uniform and distinctive in the field.Its poor representation in herbaria is probably attributable to its dwarf habit (Fig. 6) and not to its scarcity in the field as, during a recent trip to the eastern Transvaal, it was found to be locally common throughout the moist highlands.
Dr. K. D. Gordon-Gray for her guidance and advice during the initial stages of this study and for kindly providing funds for Fig. 4
. I am grateful to the Director, Botanisches Museum der Universitat Zurich, for the loan of the types of E. ellipticifolium Schinz.Ondersoek van al die beskikbare gegewens dui daarop dat Eriosema nanum Burtt Davy 'n sinoniem van E. ellipticifolium Schinz is.Die verwantskappe tussen E. ellipticifolium en E. uniflorum Burtt Davy word ook bespreek. UITTREKSEL'n