A taxonomic revision of the genus Merciera ( Campanulaceae )

A taxonomic account o f Western Cape endemic genus Merciera A.DC. is presented. Six species, supported by recent phenetic studies, are recognized. M. brevifolia A .DC., M. eckloniana H.Buek. M. leptoloba A.DC. and M. tenuifolia (L.f.) A.DC are retained as species. M. azurea Schltr. is returned to species status and M. tetraloba C.N.Cupido was recently described. Each species is described and illustrated. A key to the species, and distribution maps are provided.


INTRODUCTIO N
Merciera A.DC. is a poorly known genus o f small shrubs confined to Western Cape.South Africa.The genus is classified in the Campanulaceae subfamily Campanuloideae.This subfamily, often treated as a sepa rate family, comprises between 35 to 55 genera and 600 species (Cosner et al. 2004).In the southern hemisphere only South Africa shows great diversity with 10 genera.Eight genera are endemic to South Africa and o f these five are endemic to the Cape Floristic Region (CFR) (Goldblatt 1978).Taxonomically, genera are separated on account o f capsule structure, particularly the mode o f dehiscence.Merciera is unique amongst the South African genera in that its capsule is indehiscent.In addi tion to the unique capsule, the genus is characterized by salverform, tetramerous or pentamerous.blue-violet or white flowers and four basal ovules.
Species limits o f Merciera were re-assessed in Cupido (2003), employing phenetic methods.The results o f the phenetic studies support the recognition of six species.A taxonomic account o f Merciera based on the phenetic studies is presented here.
M ATERIAL AND M ETHODS Sampling methods, preparation and examination of study material used arc set out in Cupido (2003).In addi tion to specimens from SAM. BOL. and NBG cited in Cupido (2003), material from PRE.K and MO (acronyms as in Holmgren et al. 1990) were also examined for this revision.

Species concept
Taxonomists arc frequently criticized for not being explicit about the criteria used in species delimitation.No universal species concept exists (Davis & Goldman 1993) and it therefore depends on the individual taxonomist to define species level taxa (Cupido 2003).In this study, the criterion o f overall similarity that is based on observed patterns o f character variation is employed.This criterion has been formulated into the phenetic species concept.The phenetic species concept considers discrete clusters in character hyperspace as species.Phenetic clusters are recognized by the possession o f a particular minimum number o f characters in common.Six phenetic clusters were revealed by phenetic analysis (Cupido 2003).Each o f these clusters is considered a species.Buek (1837) added two more spe cies.but one o f these.M. heteromorpha, was erroneously placed in the genus, belonging in the Rubiaceae instead (Sonder 1865).Species described by Buek (1837) appear to have been overlooked by De Candolle (1839).Sonder (1865) reduced the genus to two species.M. brevifolia A.DC. and M. tenuifolia.which were divided into two and four varieties respectively.More than three decades later.Schlechter (1898) described a species.M azurea Schltr.from Sir Lowry's Pass.In the last comprehensive treatment o f Merciera.Adamson (1954) recognized five species, one o f which.M. tenuifolia.was divided into two varieties.In a remarkable coincidence.Adamson, like Buek before him.described a species.M. vaginata Adamson, which also belongs in the Rubiaceae (Adamson 1955).Since A dam son's treatment.Cupido (2002) added one more species from localities west o f the Hottentots Holland Mountains in the Western Cape.In the present paper, six species are recognized in total, comprising De Candolle's (1830) original three, and one each described by Buek (1837).Schlechter (1898) and Cupido (2002).None o f the species are divided into varieties.(1951) cited Merciera leptoloba A.DC. as the type species o f Merciera.in effect, an act o f lectotypification.However, according to Stafleu & Cowan (1983)

Leaves
The leaves are alternate, linear and sessile, often appearing dead due to the brown colour.The margins are entire, and usually ciliate.The abaxial surface is hairy in all species, except in Merciera tetraloba C.N.Cupido.
Leaves are variable in size and insertion along the stem.In Merciera leptoloba the leaves become smaller towards the top o f the stem.In M. tenuifolia and M. azurea the leaves are subequal and crowded, but in M. eckloniana H.Buek, they are widely spaced.
Clusters o f smaller green leaves are always present in the axils o f leaves in all species except Merciera azurea, in which they are seldom present.These leaf clusters are in fact highly reduced short shoots developed in the axils o f long shoot leaves.

Inflorescence
In an account on the inflorescence morphology o f the Campanulaceae, Philipson (1953) described the inflores cence o f Merciera as intercalary.The flowers are solitary in the axils o f foliage leaves and after producing a zone of flowers, the axis continues to grow vegetatively.This arrangement is particularly marked in M. leptoloba.
Careful examination o f the inflorescence reveals that there are in fact three flowers per axil.Only the termi nal one develops however, and the two lateral flowers remain rudimentary on highly reduced lateral branches with bract-like leaves.The terminal flower lacks a bract like leaf.The reduction o f the lateral branches gives the flowers an axillary appearance.This basic structure is repeated in the entire flowering zone, forming a spike like synflorescence towards the end o f the main branches.The order o f flowering is acropetal.

Flowers
Phenotypic plasticity is common in the Campanulaceae (Eddie & Ingrouille 1999) and Merciera is no exception to the rule.Numbers o f floral parts are sometimes vari able in the same species.Additional floral parts tend to develop, and flowers that are normally pentamerous, may become hexamerous.Both flower types are usually present on the same plant.

Calyx
The calyx is 4-or more commonly 5-lobed.Hairs are often present on the hyaline tips, but only on the margins in Merciera tetraloba.The lobes are fused at the base to form a short tube.

Corolla
The corolla is actinomorphic with a conspicuous tube and 4 or 5 spreading lobes.The corolla colour is white or blue to violet, and occasionally white-flowered species have purple tips to the corolla lobes.Tube length and flower colour is correlated, dividing the genus into two groups.White-flowered species have tube lengths less than 7 mm.whereas blue to violet-flowered species have tube lengths exceeding 7 mm.

Androecium
Stamens are 4 or 5, free, inserted at the base o f the corolla tube and included in the corolla.The filaments are flattened, wider and pilose about the middle becom ing narrower towards the apex.Anthers are linear and basifixed.

Gynoecium
The inferior ovary is surrounded by a hispid hypanthium.In accordance with the trichome terminology o f Payne (1978), four trichome types are found on the hypanthium: filiform, clavate, uncinate or circinate (Figure 1A-D).The locule number has been described as 1-or incompletely 2-locular (De Candolle 1830).However, careful dissecting o f the ovary reveals a complete but delicate septum, dividing the ovary into 2 locules.Each locule contains 2 basal ovules.The style is filiform, exserted.glabrous and inserted in a convex disc.The style is shortly divided, with the number of stigmatic lobes corresponding to the number o f locules in the ovary.
Flowering tim e: December to January. Figure 2.
Distribution and habitat: the distribution o f Merciera tenuifolia (Figure 3) is limited to Bot River, Houwhoek and Kogelberg where it is found on stony soil at altitudes ranging between 110 and 600 m.
Distribution and habitat: Merciera leptoloba is a com mon species o f the Cape southeast coast, from Kogelberg to Bredasdorp (Figure 8).This species is found on sandy or stony flats and hills at altitudes ranging between sea River, Houwhoek, Shaw 's Mountains and the Caledon Swartberg (Figure 10).
On the Houwhoek Mountains where this species occurs in sympatry with Merciera leptoloba, possible hybrids between the two species are formed.Flats in Strand, the few existing populations are under serious threat of extinction.

Excluded species
Merciera heteromorpha H.Buek = Carpacoce heteromorpha (H.Buek) Bolus When Buek (1837) described the species, he noted that it most likely constituted a distinct genus.Sonder (1865) considered it a member o f Rubiaceae, but did not treat it taxonomically.A few decades after Sonder, Bolus (1896) transferred the species to the genus Carpacoce in the Rubiaceae, where it is currently classified.

Merciera vaginata
TAXONOM IC HISTORY De Candolle ( 1830) established the genus Merciera to accommodate three species o f Campanulaceae from the Cape characterized by having four basal ovules in uniloc ular or incompletely two-locular ovaries, and indehiscent capsules.One o f these species.M. tenuifolia (L.f) A.DC. had previously been placed in either Trachelium L. or Roella L., the other species were newly described.The genus was named in honour o f botanist Phillip Mercier who wrote a monograph on the family Polemoniaceae.Initially De Candolle described the genus as 'incertae sedis' because o f the unusual structure o f the ovary, but later classified it in the m onogenenc tribe Merciereae (De Candolle 1839).
The locality o f the specimen MacChvan 3103 (SAM) collected at Tulbagh Nuwekloof is suspect.It has the same locality, collecting date and number as a specimen o f M. azurea.No recent collections o f .V/. tenuifolia have been made in the Tulbagh area.Conservation status'.Vulnerable D2 (World Conser vation Union [IUCN] 2001).
Pfeiffer (1874))frequently indicated type species for generic names, which constitute in numerous instances, the first selection o f a lectotype.For the genus Merciera, Pfeiffer (1874) cited only Trachelium tenuifolium, the basionym o f M. tenuifolia (L.f.) A.DC. Single species are mentioned only when they serve as a type o f new' genera or sections, as was done with Merciera.