Two new species of Gladiolus ( Iridaceae : Ixioideae ) from South Africa and notes on long-proboscid fly pollination in the genus

G ladiolus rhodan thus is a new species known from a single population on the summit o f the Stettynsberg near Villiersdorp in Western Cape. South Africa The species most closely resembles G. hirsutus and G caryophyllaceus but dif­ fers from both in flower shape and markings and in its ecology and reproductive biology. It forms part o f a guild o f longtubed, pink-flowered species including Erica praecox, Pelargonium radiatum and Watsonia paucifolia which are pollinat­ ed by an undescribed long-proboscid fly. M oegistorhynchus sp nov. (Diptera : Nemestrinidae). G ladiolus sekukuniensis is a new species known from three populations south o f the Strydpoortberge in Northern Province It closely resembles G. perm eahilis subsp edulis in vegetative features and in flower form, but differs from it in flower colour and in the elongate peri­ anth tube. These floral features are apparently adaptations to pollination by long-proboscid flies.


INTRODUCTION
Arguably the largest genus in the family Iridaceae.Gladiolus contains some 260 species distributed throughout Africa and Eurasia as far east as Afghanistan, but its greatest centre of diversity is in southern Africa.Some 165 species occur in the subcontinent, of which 159 are endemic there (Goldblatt & Manning 1998).Within the subcontinent several centres of endemism have been identified (Goldblatt & Manning 1998).By far the greatest number of species occurs in the southwest ern corner, the centre of the southern African winter rain fall region.This is an area of high topographic and edaphic diversity in which local endemism is highly developed.Many of these endemics are restricted to a single isolated massif or mountain range.It is not alto gether surprising, therefore, that a new species of Gladiolus should be discovered on a high mountain bare ly four months after the publication of a comprehensive revision of the genus (Goldblatt & Manning 1998).A second centre of diversity, the Wolkberg centre, lies at the opposite end of the subcontinent in the highlands of Mpumalanga and Northern Province.This is a region of great geological complexity, and local endemism within the genus here is largely the consequence of the high edaphic diversity.Substrates favouring endemism in clude sandstones or quartzites, dolomite and serpentine.The discovery of another apparent edaphic endemic from the northern part of the region emphasises the impor tance of substrate in promoting speciation in Gladiolus throughout the subcontinent.Species of Gladiolus are highly diverse in floral form and much of this variation is related to their pollination biology.Although bees are known or inferred to pollinate about 56% of the species in the genus (Goldblatt et al. 1998), one of the most important pollinators of the remainder are long-proboscid flies in the families Nemestrinidae and Tabanidae.This pollination strategy is uniquely well developed in southern Africa and numerous late spring-and summer-flowering plant species throughout the subcontinent have exploited it (Goldblatt & Manning in press).Southern African species of Gladiolus pollinated by long-proboscid flies typically have unscented, long-tubed cream or pink flow ers marked on the lower tepals with red (Goldblatt & Manning 1998, 1999).The flowers of both species of Gladiolus described here conform exactly to this pattern and although pollination by long-proboscid flies has been confirmed in only one of the two species, it is inferred to occur in the second.Gladiolus rhodanthus J.C.Manning <£ Goldblatt.sp.nov.Plantae 300-500 mm altae, cormo globoso 18-25 mm diametro tunicis fibris tenuibus verticalibus, foliis 3 pubescentibus.folio infimo basali lamina lineari 1.5-2.0mm lata, costa incrassata marginibus vix incrassatis, caule eramoso, spica leviter flexuosa 2-5-flora, bracteis 26-45 mm longis.floribus atroroseis tepalis inferioribus stria albida hastiformi ornatis, tubo perianthii oblique infundibuliformi 25-36 mm longo.tepalis inaequalibus lanceolatis, tepalo dorsali 35-40 x 19-24 mm.inferioribus 27-30 x 11 mm.filamentis 15-17 mm longis.antheris 8-9 mm longis.Plants 300-500 mm high.Corm globose, 18-25 mm diam.. tunics of medium-textured to fine vertical fibres, accumulating with age and forming a neck around base of stem.Stem erect, flexed outward above sheath of second leaf and inclined ± 30°, unbranched, 1-2 mm diam.below spike.Cataphxlls pale and membranous, the uppermost dark green or purple above ground or sometimes dry.Leaves 3. lower one or two basal, the second of these sheathing lower half of stem, pubescent throughout, low ermost longest with blade reaching to between base and apex of spike, sometimes becoming dry at flowering time, the second with blade rather short and reaching upper third of stem, blades plane, more or less linear.3-6 mm wide, midrib thickened and raised and a second pair of veins lightly thickened, margins scarcely thickened, the upper most leaf inserted on upper third of stem, short, sheathing for half to two thirds of its length, blade vestigial, pubes cent.Spike inclined, lightly flexuose, 2-to 5-flowered; bracts green or flushed brownish above, outer 26-45 mm long, acute, inner two thirds or rarely about as long as outer, lightly notched.Flowers deep pink, lower three tepals each with a spear-shaped whitish median streak in lower half edged in dark pink, especially in upper half, sometimes darker edging expanded transversely across entire width of upper laterals, throat white with a few dark pink streaks, unscented; perianth tube 25-36 mm long, cylindrical below for 20-28 mm, obliquely expanded in upper 5-7 mm, shortly exceeding bracts; tepals lanceolate, unequal, dorsal largest, inclined over stamens, 3 5 ^0 x 19-24 mm, upper laterals slightly shorter, 30-38 x 13-19 mm, recurved in upper half, lower three tepals joined to upper laterals for 5 mm and to one another for 1-2 mm, ± horizontal below, sharply flexed downward in middle, 27-30 x 12-13 mm. in profile lower tepals exceeding upper by 5-10 mm.Filaments 15-17 mm long, exserted 8-10 mm from tube; anthers 8-9 mm long, light mauve; pollen cream-coloured.Ovary-oblong, ± 6 mm long; style arching over stamens, dividing at or slightly beyond apices of anthers, branches spreading, 5-7 mm long.Capsules ellipsoid, 20-22 x 8-9 mm.Seeds broadly and evenly winged, golden-brown.5.5-7.0 x 4 mm.Chromosome number: unknown.Flowering time: late December to mid-January.Figure 1; Plate 1.
Distribution and biology: Gladiolus rhodanthus is known from a single large population on the Stettynsberg near Villiersdorp (Figure 2).The plants are restricted to broken sandstone cliffs on warm north-facing slopes at an altitude of 1 800 m where the corms are wedged in cracks in a peaty loam.Frequent summer cloud driven by strong southeasterly winds is a feature of many of the high mountains in the southwestern Cape.At this altitude and in this situation the soil around the corms of G. rho danthus is still moist in the middle of summer when the plants flower.
The flowers of Gladiolus rhodanthus are pollinated by the fly, Moegistorhynchus sp.nov.(Nemestrinidae) which has a slender proboscis ± 20 mm long.There is a close fit between the shape of the flower and the body of the fly.The head and thorax of the fly fit snugly into the upper part of the tube when its proboscis is fully insert ed into the lower part.In this position the dorsal thorax brushes against the anthers and style branches while it forages for nectar held in the lower third of the tube.
Several other plant species with long-tubed, similarly coloured flowers co-occur with G. rhodanthus and arc also pollinated by this fly.They include Erica praecox, Pelargonium radiatum and Watsonia paucifolia.The convergence in flower colouring and perianth length between these plant species at this locality is a striking example of the effect that specialist pollinators can have on flower form.At the time of its description, the longtubed flowers of W. paucifolia were contrasted with the funnel-shaped blooms of the closely related species W. distans which was thought to be pollinated by bees (Goldblatt 1989).It was already then recognised that the tubular flowers of W. paucifolia were probably spe cialised for pollination by a different agent, but no infor mation on its pollination biology was available.The recent collection of the pollinator and associated guild members has vindicated this idea.More than one plant species which share a single long-proboscid fly as the pollinator often co-occur and converge in their floral morphology to form a local guild of species (Manning & Goldblatt 1996, 1997).Because of the potential dangers of interspecific pollen transfer in such guilds, pollen is invariably placed by different guild members on differ ent parts of the pollinator's body.This is clearly demon strated in the Stettynsberg guild: G. rhodanthus deposits pollen on the dorsal surface of the thorax, W. paucifolia on the top of the head, E. praecox on the face and F. radiatum on the underside of the thorax.
History: the species was apparently first encountered by botanists Ted and Inge Oliver in December 1997 on an expedition to collect a species of Erica high on the Stettynsberg to the north of Villiersdorp.Unfortunately no specimens were collected but the following year they revisited the locality accompanied by the natural history photographer, Colin Paterson-Jones, who collected a sin gle plant.This specimen was quite unlike any known species of Gladiolus and another expedition was imme diately organised in order to examine the plants in the field and to collect the type material.The Stettynsberg is one of the highest mountains in the greater Hottentots Holland chain, reaching just over 1 800 m at the summit, and until recently has not been accessible except by foot.The late flowering of G. rhodanthus is probably the rea son that it was not seen by the indefatigable Cape botanist Elsie Esterhuysen, who first visited the moun tain in 1948, and only a chance encounter with spent plants of Erica schoemannii in September 1998, prompt ed the Olivers to revisit the mountain in December.
Diagnosis and relationships: the three superposed leaves with hairy sheaths and hairy blades with a welldeveloped pair of secondary veins place G. rhodanthus in series Linearifolius of section Linearifolius.This series now contains 12 species, all restricted to sand stone-derived or granitic soils in the winter rainfall region.Radiation in the series is associated with exten sive floral adaptation for specialised pollination strate gies.In addition several species flower unusually late in the season during the summer, the dry season in most of Western Cape.Within the series the relationships of G. rhodanthus are less clear.Although most likely to be confused with the short-tubed and smaller-flowered G. hirsutus Jacq., the similarities between the two species are largely plesiomorphic and G. rhodanthus may be more closely allied to the species with an elongate peri anth tube such as G. caryophyllaceus (Burm.f.) Poir.or G. guthriei F.Bolus.
Gladiolus rhodanthus is readily distinguished from the two other South African species of Gladiolus with well-developed hairy leaves and pink flowers, G. hirsu- The marked floral differences between these species are linked to differences in their floral ecology.The fun nel-shaped flowers of G. hirsutus and G. caryophyl laceus are typical of bee-pollinated species of Gladiolus and those of the former, at least, are visited by species of Apis and Anthophora (Hymenoptera: Apidae) (Goldblatt & Manning 1998;Goldblatt et al. 1998) whereas the more tubular flowers of G. rhodanthus are typical of species which are adapted to pollination by long-proboscid flies.In floral morphology G. rhodanthus is actu ally similar to another quite unrelated fly-pollinated species, G. virgatus Goldblatt & Manning (section Homoglossum).Shifts between pollinators among relat ed species of Gladiolus are common and occur repeated ly throughout the genus.In this regard it is striking to note the floral similarity between both the bee-pollinated and long-proboscid fly-pollinated members of the species pairs G. hirsutus-G.rhodanthus (section Lineariolius) and G. blommesteinii L.Bolus-G.virgatus (sec tion Homoglossum).
In a genus characterised by pollinator-driven floral diversity, series Linearifolius is particularly noteworthy for the frequency of derived pollination strategies (Goldblatt & Manning 1998).Out of the 12 species now recognised in the series only two or three are bee-polli nated, the plesiomorphic pollination strategy for the sec tion and the genus.The remaining species have various derived pollination strategies including pollination by moths, long-proboscid flies, birds and the butterfly Aeropetes tulbaghia (L.).This strong shift to derived polli nation strategies and. in many cases, late or aseasonal tus or G. caryophyllaceus, by the shape and markings of its flowers and by its late flowering time.Intermediate between these two species in size, the flowers of G. rho danthus differ from both in their elongate perianth tube, 25-36 mm long, which is cylindrical for most of its length and flares only in the upper 5-7 mm, the lanceo late and acute tepals with plane margins and the median white lozenge-shaped marking outlined with red on each of the lower tepals.The flowers of G. hirsutus and G. caryophyllaceus are obliquely funnel-shaped and flared in the upper half, the tepals are ovate and obtuse, usual ly with undulate margins, and the lower tepals are irreg ularly streaked and spotted with red on a pale back ground.Although nearest G. caryophyllaceus in flower size, G. rhodanthus is also readily separated from this species by its unthickened leaf margins and shorter fila ments, 15-17 mm long versus 22-27 mm long.It is most flowering times, suggests that section Linearifolius entered the winter rainfall region relatively late in the history of the genus, at a time when most of the springflowering, bee-pollinated niches were already occupied by other species of Gladiolus, in particular those of sec tions Hebea and Homoglossum (Goldblatt & Manning 1998).Both of these sections have diversified strongly in the winter rainfall region, the former mainly on clay soils and the latter on sandstone-derived soils, and contain a preponderance of bee-pollinated species.The discovery of G. rhodanthus, another species in series Linearifolius which is both late-flowering and adapted to a specialised pollination strategy, provides further support for this hypothesis.
G. rhodanthus can be accommodated in the keys in the recent monograph, Gladiolus in southern Africa (Goldblatt & Manning 1998) by inserting the following couplet into both the key to section Linearifolius and the key to Gladiolus in the winter rainfall region of southern Africa, at leads 14' (p.53) and 33' (p.64) respectively.Plants 0.6-1.1 m high.Conn globose to conic, 8-15 mm diam., mostly producing cormlets on suckers to 100 mm long from base, suckers with scattered amplexicaul scales, tunics of fine-textured fibres.Stem erect, flexed outw'ards above sheath of fourth leaf, simple or with one or rarely more branches, 0.8-1.2mm diam.below spike.Cataphylls pale and membranous, uppermost dark green or dry.Leaves usually 5-7.sometimes more, lower three to four basal, lower three usually reaching to at least base of spike or exceeding it; blades linear, (l-)2 -4 mm wide, rigid, midrib thickened and raised, margins sometimes lightly thickened, cauline leaves shorter than basal, uppermost without a blade and sheathing for most of its length, lower margins free almost to base.Spike inclined, lightly flexuouse, 8-17-flowered; bracts cream-coloured or pale grey-green, flushed pinkish above, dry and pale near apices, the outer (14-) 17-21 mm long, acute, the inner two thirds to almost as long as outer, acute or light ly notched.Flowers white or cream-coloured to pale salmon-pink, tepals each with a narrow, dark red, longi tudinal median streak, often lacking or incomplete on dorsal tepal, lower tepals sometimes with yellow streak in centre, unscented; perianth tube (22-)25-35 mm long, cylindrical below for 20-30 mm.curved and weakly flared in upper 5-6 mm, much exceeding bracts; tepals unequal, all narrowed below into claws and more or less spade-shaped, attenuate and with twisted and undulate tail-like tips, dorsal largest, inclined over stamens, arch ing upward near apex, 25-35 x 8-11 mm, claw ± 5 mm, upper laterals directed forward, arching outward in upper half, 19-25 x 4.0-4.5 mm, claw ± 7 mm, windowed between bases of dorsal and upper lateral tepals, lower three tepals joined to upper laterals for 1.5-3.0mm and to one another for 2.5-4.0 mm, with small thickened knobs at sinuses between lower tepals, free parts 15-18 x 1.5 mm, narrowed below into channelled claws 3-4 mm long, abruptly flexed downward into a narrowly lanceolate limb, in profile lower tepals exceeding upper.Filaments 10-12 mm long, exserted 6-8 mm from tube; anthers 5.0-6.5 mm long, dull blue; pollen creamcoloured.Ovary oblong, 3.5-4.5 mm long; style arching over stamens, dividing between middle and apices of anthers, branches, 1.5-2.0mm long.Capsules ovoidellipsoid, 12x7 mm.Seeds ovate, 6.5 x 4.0 mm, translu cent light brown, seed body dark brown, large in relation to the wing.Chromosome num ber unknown.Flowering time: March to April. Figure 3.
Distribution and biology: Gladiolus sekukuniensis is known from two sites in Sekukuniland, west of the Transvaal Drakensberg (Figure 2).It grows in open woodland on the Strydpoortberge and nearby Leolo Mountains overlooking the upper Olifants River Valley.In both localities the species grows on alkaline soils.On the Strydpoortberge it occurs among Acacia caffra and Combretum molle on banded ironstone in soil contain ing lumps of calcrete associated with the surrounding dolomite, while on the Leolo range it occurs on norite with Kirkia wilmsii and Catha transvaalensis (another Sekukuniland endemic).Non-flowering plants are diffi cult to see among the tufts of Theme da triandra with which they are often associated.In form and colouring the flowers of G. sekukuniensis are highly reminiscent of those of G. macneilii Oberm.(section Densiflorus: series Calcaratus), a local edaphic endemic restricted to adjacent dolomite hills where the Olifants River cuts through the Transvaal Drakensberg.This species is known to be pollinated by the long-proboscid fly Stenobasipteron wiedemannii (Nemestrinidae) (Goldblatt & Manning 1998, 1999).The flowers of G. sekukunien sis conform to this pollination syndrome in morphology and flowering time and are apparently adapted to pol lination by the same or another long-proboscid fly species.Several species of Gladiolus endemic to the Wolkberg centre of endemism in the highlands of Mpumalanga and Northern Province are adapted to pol lination by long-proboscid flies in the family Neme strinidae and these flies are clearly an important factor History: first reported in 1997 from the Leolo Mountains by Sylvia Thompson of Haenertsburg, Gla diolus sekukuniensis was then collected from the Bewaarkloof area in the southern foothills of the Strydpoortberge in 1999, and subsequently from the pop ulation on the Leolo Mountains.Mervyn Lotter, a botanist with Mpumalanga Parks Board, has also reported the species from the same general area, bringing the number of known populations to three.
Diagnosis and relationships: the narrowly linear leaves without conspicuously thickened margins or evi dent secondary veins and the distinctively windowed flowers (in profile gaping between the dorsal and upper lateral tepals) with the tepal apices conspicuously tailed, indicate a very close relationship between G. sekuku niensis and G. permeabilis subsp.edulis (Burch, ex Ker Gawl.)Oberm.(section Hebea, series Permeabilis).Although widespread throughout southern Africa, G. permeabilis does appear to have been recorded from Sekukuniland itself.It occurs on a variety of soil types, from deep Kalahari sands to fine-grained doleritic clays, but apparently not on dolomitic or other alkaline soils.The two species can be distinguished on details of flower colour and markings and in the length of the perianth tube.In addition, the suckers commonly produced from the base of the corm in G. sekukuniensis are unknown in G. permeabilis.The flowers of G. permeabilis subsp.edulis vary from a pale yellowish cream colour to dull purple, the lower tepals usually each with a narrow medi an yellow marking outlined with purple, and the perianth tube is obliquely funnel-shaped, shorter than the dorsal tepal and 9-15 mm long.The flowers of G. sekukunien sis are white or cream-coloured to pale salmon pink, each of the tepals with a median dark red streak, and the perianth tube is cylindrical, longer than the dorsal tepal and 22-35 mm long.
The species may also be confused with G. niacneilii on account of the general resemblance in floral form between the two, but the flowers of G. niacneilii are not windowed in profile because the tepals are not clawed, the upper lateral tepals are not marked, the perianth tube is rather longer, 40-45 mm long, and the anthers are dis tinctly tailed at the base.
G. sekukuniensis can be accommodated in the keys in the recent monograph Gladiolus in southern Africa (Goldblatt & Manning 1998) by inserting the following couplets into the key to section Hebea at lead 29 (p.55) and into the key to Gladiolus in Botswana, northern Namibia, the northern provinces of South Africa and Swaziland at lead 21 (p.59) respectively.

FIGURE I.-G ladiolu s rhodanthus. A, corm with cataphylls; B, flowering spike; C, leaf; D. flower, front view; E, half-flower. Scale bar: 10 mm. Artist: John Manning. likely
to be confused with G. hirsutus but this species has shorter bracts, 18-26 mm long versus 26-45 mm long, and shorter filaments, 11-13 mm long versus 15-17 mm long.In addition G. rhodanthus is distinct from these species in its habitat on broken cliffs at high altitude and late flowering time in December and January.G. hirsu tus is a common species on stony granite or sandstone slopes and flowers mostly between July and September or rarely in March or April while G. caryophyllaceus favours dry habitats on open sandstone or granite slopes or in deep sands and flowers between August and September.