The genus Wellstedia ( Boraginaceae : Wellstedioideae ) in southern Africa

This regional taxonomic revision of the genus Wellstedia Balf.f., a member of the family Boraginaceae s.I. (including Hydrophyllaceae s.str.), is part of a series of publications on the Boraginaceae in southern Africa. Wellstedia comprises six species, five in Socotra, Somalia and Ethiopia with the remaining one. W. dinteri Pilg.. occurring in southern Africa. W dinteri Pilg. subsp. dinteri occurs in Namibia and the Northern Cape, whereas the newly instated subspecies W. dinteri subsp. gracilior (D.R.Hunt) Retief & A.E.van Wyk, based on W. dinteri Pilg. var. gracilior D.R.Hunt, is confined to Namibia only. The disjunct distribution of Wellstedia and numerous other plant and animal taxa between the arid regions of northeastern Africa and southern Africa is usually explained by the postulated periodic existence of an arid corridor between the two regions during the arid phases of the Pleistocene and even earlier. Wellstedia is treated here in Wellstedioideae, a subfamily of Boraginaceae s.I. but is sometimes placed in a family of its own, Wellstediaceae Pilger. Morphologically Wellstedia displays strong similarity to genera of the Ehretioideae and also to certain members of the Hydrophyllaceae. The genus is characterized by a perennial, dwarf shrub habit, densely hairy leaves. 4-merous flowers, a terminal, bifid style and a 1or 2-seeded capsule. A key to the two subspecies, diagnostic characters, a distribution map and illustrations of various macroand micromorphological features are provided.


INTRODUCTION
Wellstedia was described in 1884 by Balfour after a visit to the island of Socotra.He decided on the name Wellstedia in honour of the British Lieutenant J.R. Wellsted, who explored Socotra for the Indian Government in 1834 (Thulin & Johansson 1996).Balfour believed that W socotrana Balf.f., the only species in the genus at the time, had its closest affinity with members of Boraginaceae s.str.Besides this spe cies, five more are now recognized on the African conti nent-four in Somalia and Ethiopia, and one in Namibia and South Africa.Such floristic (and faunistic) disjunc tions between the arid regions of northeastern Africa and southern Africa are usually ascribed to the periodic exis tence of a linking arid corridor between the two regions in the past (Van Wyk & Smith 2001).In 1912 Pilger placed Wellstedia in its own subfamily, Wellstedioideae (Boraginaceae).Novak (1943), however, decided on a separate family, Wellstediaceae.Since then, the family classification of Wellstedia has been a matter of contro versy.Merxmiiller (1960), unaware of Novak, also estab lished a new family, Wellstediaceae, thereby creating a later homonym.In 1967 the family was also recognized by Friedrich-Holzhammer in a Prodromus on the flora of South West Africa [Namibia], an approach more recently followed by Lebrun & Stork (1997).
Different modem views regarding the delimitation of Boraginaceae exist: splitting Boraginaceae s.I. into two separate families.Boraginaceae.v.str.and Heliotropiaceae with Hydrophyllaceae not included (Diane et al. 2002); or recognizing several segregate families, Boraginaceae s. str., Cordiaceae, Ehretiaceae, Heliotropiaceae, Hydro phyllaceae, Lennoaceae and Wellstediaceae (Lebrun & Stork 1997;Gottschling et al. 2001;Gottschling 2003).In the present contribution.Wellstedia is regarded as a monotypic genus of the subfamily Wellstedioideae with in Boraginaceae s.I. (including Hydrophyllaceae s.str., Codonoideae.Ehretioideae.Heliotropioideae and Boraginoideae) (Retief 2003).Ferguson (1999) and the Angiosperm Phylogeny Group II (2003) are followed here in regarding the tribes Phacelieae and Hydrophylleae as part of Boraginaceae s.I.The capsular fruit of Wellstedia is unknown elsewhere in Boraginaceae s.str.and has been used to motivate the recognition of a monotypic family Wellstediaceae.However, with members of Hydrophyllaceae.all with capsular fruits, included in a broadly defined Boraginaceae, this argument is no longer of importance.Pollen and other characters such as a ter minal style.4-merous flowers, trichomes with multicellular bases and cymose inflorescences similar to other tra ditional members of Boraginaceae, support the placement of Wellstedia in a subfamily within Boraginaceae s.I.
The aim of this paper is to present a taxonomic revi sion of the genus Wellstedia in southern Africa, includ ing Namibia.Botswana.South Africa.Lesotho and Swaziland.Diagnostic characters, an identification key, illustrations and a distribution map are provided.This paper forms part of a revision of the Boraginaceae in southern Africa.The genus description is based on mate rial from southern Africa only.

MATERIALS AND METHODS
Herbarium specimens in BM.BOL, E, GRA, K. NBG, NH.NU.PRE.PRU, SAM and WIND (acronyms as in Holmgren et al. 1981) were studied to gather data on morphological characters, phenology and geographi cal distribution.Pollen and various plant parts were stud ied with an ISI-SX-25 scanning electron microscope.Measurements of pollen grains were done from aceto-lysed grains mounted in glycerine jelly.Acetolysis fol lowed the standard method of Erdtman (1960).Tapetal orbicules were obtained from herbarium specimens and prepared for viewing with a JEOL 6000 F in-lens field emission scanning electron microscope (for procedure followed see Retief et al. 2001Retief et al. , 2002)).

HISTORICAL OUTLINE
In 1912, Pilger described W. dinteri from specimens collected by botanist and botanical explorer Moritz Kurt Dinter  in Namibia.Although Pilger knew the genus only from Balfour's (1884) description and illustration of W. socotrana, he was convinced that Dinter had found a Wellstedia in the southwestern part of Africa.He was also of the opinion that Wellstedia belongs to Boraginaceae with affinity to Coldenia L. of the Ehretioideae, and not Verbenaceae, a family also metioned by Balfour (1884) when he described the first species.The capsular fruit with two seeds, however, distinguishes Wellstedia from all other members of Boraginaceae and a new subfamily Wellstedioideae was described by Pilger (1912).
Variety dinteri is characterized by flowers and cap sules congested on short lateral branches, whereas var.gracilior has flowers and capsules on lax branchlets, appearing as if solitary, axillary, rarely close together.When Friedrich-Holzhammer (1967) revised the genus for Prodromus einer Flora von Sudwestafrika, she did not recognize the two infraspecific taxa proposed by Hunt (1969) and regarded W. dinteri as belonging to Wellstediaceae.Thulin & Johansson (1996), in a revi sion of the genus, also did not maintain the two varieties in W. dinteri.They classify the genus in Wellstedioideae and proposed the New World genus Tiquilia Pers.(Boraginaceae: Ehretioideae) as a possible sister to it.In the present revision, the status of W. dinteri Pilg.var.gracilior D.R.Hunt is raised to that of subspecies, a deci sion based mainly on differences in macromorphology and habitat.

PHYTOGEOGRAPHY
The two subspecies of Wellstedia dinteri in southern Africa (Figure 1) are associated with the Nama-Karoo, Succulent Karoo and Savanna Biomes, according to the biome map in Van Wyk & Smith (2001: 8 ).W. dinteri subsp.dinteri is recorded as growing in shale-derived soil mixed with fine gravel (Davidse & Loxton 6339).W dinteri subsp.gracilior, however, occurs on dolomite or limestone (Acocks 15641) or on black soil derived from dolomite.
Arid regions of the African continent are phytogeographically linked by a large number of taxa with dis junct distributions.This pattern is particularly well developed between arid regions in southern Africa and northeastern Africa (Horn of Africa and adjacent Arabian Peninsula).Wellstedia is a typical example of a taxon with a disjunct distribution between the arid areas of northeastern Africa and southern Africa: W din-  Thulin (1994) and Thulin & Johansson (1996) also commented on the recurring pattern of disjunct distributions.Gaillonia A.Rich, ex DC. (Rubiaceae), as circumscribed by Thulin (1998), is another example of a genus with a disjunct distribution comparable to that of Wellstedia (Thulin 1994).
Disjunct distributions in Africa and the New World are rather unusual, but for southern Africa, as many as seven families and many more genera are involved (Goldblatt 1978).Codon L., an exclusively southern African genus, has its nearest relatives, members of Hydrophyllaceae s.str., in North America.However, Wellstedia also shows similarities in pollen and habit characters with some of the genera of Hydrophyllaceae s.str.A possible explana tion for this disjunct distribution pattern is the existence of a Tertiary North Atlantic land bridge (Tiffney 1985), whereas over-water dispersal seems unlikely, except dur ing the early stages of continental separation.

Habit
Members of the Boraginaceae are mainly herbaceous, but shrubs and trees do occur.Wellstedia is characterized by a woody, dwarf shrub habit, a growth form also dis played by Tiquilia. of the subfamily Ehretioideae-sug gested as a potential sister group of Wellstedia (Thulin & Johansson 1996).The woody habit and other morpholog ical similarities with the Ehretioideae support the classi fication of Wellstedia as a member of the Boraginaceae s.I. instead of placing it in a family of its own.

Leaves
The narrowly obovate to ovate leaves of the southern African species with its two subspecies are densely pubes cent (Figure 2A, B).The trichome complement consists of rigid setae with multicellular bases, usually 3-layered, scat tered on the blade (Figure 2C) and fine setae with undevel oped bases.Leaves of Wellstedia dinteri subsp.gracilior are smaller in size and different in colour, greyish white compared to yellowish green in W. dinteri subsp.dinteri.

Flowers
Flowers of Wellstedia are 4-merous (Figure 2D), a state which is rare in Boraginaceae s.I.It is often used to support the recognition of a separate family, Wellstediaceae.However, the flowers of Coldenia, a monotypic genus and also a member of the Ehretioideae, is similarly 4-merous.This is another link between Wellstedia and a member of Boraginaceae s.I.The calyx is deeply lobed and accrescent in fruit (Figure 2L).The outer surface of the corolla is densely pubescent (Figure 2D), but the inner surface is glabrous (Figure 2E).A ter minal style is present (Figure 2F), persistent (Figure 2L) and slightly bifid with capitate stigmas, the latter covered with exudate when receptive (Figure 2F).

Fruit and seed
All members of Wellstedia are characterized by hairy, mussel-like capsules (Figure 2G, H, J, K), but differ in dissepiment morphology (Thulin & Johansson 1996).The seeds (Figure 21) are truncate, and pitted above with a circle of long, rigid trichomes in the upper part.

Pollen
Pollen grains (Figure 3A-F) of Wellstedia are tricolporate, isopolar and with mesocolpial concavities (some times regarded as 'pseudocolpi') and a reticulate tectum, showing strong similarity with genera of the subfam ily Ehretioideae (Retief & Van Wyk 2001).Wellstedia and members of Ehretioideae furthermore show simi larity in their pollen morphology with members of the tribes Hydrophylleae and Phacelieae of the family Hydrophyllaceae, here regarded as part of Boraginaceae s.l.Doughnut-shaped tapetal orbicules (Retief et al. 2001: fig.2), occur in both Wellstedia and Codon, con firming the close relationship of these genera.

Key to subspecies
Flowers and capsules congested on short lateral branchlets; leaves yellow ish green.10-50 x 3.5-6.0mm: leaf blade surface with multicellular-based setae prominent and an under layer of fine setae with undeveloped bases.Illustration '. Hunt: t. 3666 (1969).Figure 4.
Dwarf shrub, up to 300 mm high, with pseudodistichous branching.Stems procumbent, decumbent or ascending.Leaves yellowish green, 10-50 x 3.5-6.0mm; leaf blade with multicellular-based setae, distinctly spaced, and an under layer of fine trichomes prominent.Corolla pink, white or pale rose in centre, white along margins; tube ± 1 mm long.Flowering time: April to May, August to October.
Distribution and habitat: Wellstedia dinteri subsp.dinteri is found in Namibia and Northern Cape (Figure 1).It occurs on arid, gravelly hillocks, in shallow soil betw een rocks and stones.
Distribution and habitat: Wellstedia dinteri subsp.gracilior is found in Namibia (Figure 1).It occurs on rocky hillsides, black rocks and broken veld on dolo mite.