Sparaxis

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Plant morphology and floral phenology. — Species of Sparaxis are seasonal, corm-bearing geophytes of small to moderate size, with spicate inflorescences typically 10-30 cm high, but up to 60 cm in S. auriculata . Individuals produce one or more simple or branched flowering stems annually and flowering is closely synchronized in a population. Flowering occurs in late winter and spring (July to October) ( Table 2 View Table 2 ) which coincides with the period of optimal plant growth, during or soon after the main rainy season.

Flower buds open acropetally on an inflorescence. In all species a mature bud expands in the early to mid-morning and the open perianth typically lasts three or four days. Flowers open sequentially, usually one or two days apart; hence, there are often three or four flowers open at any time on an inflorescence. At sunset the flowers close, sometimes incompletely, but usually enclosing the anthers and stigmas. Flowers open again in the early morning, between 8.00 and 9.00 hours, depending on temperature.

Flowers of all species studied show weak mechanical protandry. The anthers dehisce longitudinally within one to four hours after the tepals first unfold but this depends to some extent on ambient temperature and humidity. Anthers may dehisce later the same day under wet, cool conditions. The three stylar lobes, the distal adaxial surfaces of which comprise the stigmas, are held together when the flower first opens and they diverge later during the same day. Once they have diverged, pollen will adhere to their slightly sticky surface.

Compatibility and self-pollination. — Studies of pollen-stigma compatibility of most species conducted under greenhouse conditions confirm the conclusions of HORN (1962) who showed that some species of Sparaxis are self-compatible ( Table 2 View Table 2 ). Mechanical selfing is facilitated in most species by the absence of spatial separation of anthers and stigmatic surfaces after the style branches diverge. Specifically, the style divides opposite the lower half of the anthers and the lobes extend between the anthers, thus contacting the pollen directly. However, S. auriculata , S. caryophyllacea , S. galeata and S. variegata fail to set seed when self-pollinated by hand. In these species, coincidentally, the style divides at or shortly above the apex of the anthers, the style branches arch outward for up to 3 mm, and the style lobes do not contact the anthers or pollen (see illustrations in GOLDBLATT 1992).

Floral presentation and attractants. — Open flowers are typically held erect to suberect in a spike. Flowers are arranged helically in species with actinomorphic perianths or are secund in species with bilabiate perianths. Sparaxis auriculata , S. caryophyllacea , and usually S. galeata and S. parviflora have sweetly scented flowers, with an odor reminiscent of commercial Viola odorata . In some populations of S. galeata and S. parviflora the flowers appear to lack floral odor; those of S. villosa are consistently unscented. Flowers of S. fragrans have a musky, slightly bitter odor, unpleasant to the human nose. Flowers of all species have a well developed perianth tube ( Table 2 View Table 2 ), ranging from ca. 8 mm in length in S. elegans , S. pillansii , and S. tricolor to 45-55 mm in S. metelerkampiae . Tubes are funnel-shaped with a narrow, tubular basal part 1-2 mm in diameter in species with radially symmetric flowers, or the tube may be cylindrical and elongate for up to 40 mm, then widening into a funnel-shaped upper part.

Floral colors and perianth shapes fall into four main categories ( Table 2 View Table 2 ). In the first group, of which Sparaxis auriculata and S. villosa are typical examples, flowers are moderate in size, have a short, funnel-shaped floral tube and a zygomorphic, bilabiate perianth with a hooded dorsal tepal. The perianth is violet or mauve with the throat creamy yellow and the lower three tepals bright yellow, sometimes with contrasting violet tips. These flowers usually deposit nectar in the lower half of a hollow perianth tube. We were unable to detect nectar in flowers of S. galeata , and even when cut stems of this species were maintained in the laboratory in a flask of water the flowers did not produce nectar. Sparaxis parviflora is unusual in having particularly small flowers either colored purple and yellow, or more often cream with yellow lower tepals.

In the second group, the floral tube is elongate and the flowers are scentless, have an erect, flaglike dorsal tepal, and are either violet and yellow ( Sparaxis variegata ), cream with purple markings on the upper lateral tepals ( S. roxburghii ), or deep purple with pale streaks on the otherwise purple lower tepals ( S. metelerkampiae ).

The remaining two groups of species have radially symmetric, bowl- or salver-shaped, perianths but Sparaxis bulbifera and S. grandiflora have unilateral stamens. In S. bulbifera the perianth tube is 14-16 mm long, hollow, and contains nectar. The remaining six species of this group have a tube in which the walls tightly sheath the style, and only traces of nectar are present at the mouth of the tube. The flowers are uniform in color (cream to yellow, but purple in S. grandiflora subsp. grandiflora ) or scarlet to salmon pink and then with contrasting markings in the center. Sparaxis elegans is unusual in having brown, twisted, sigmoid anthers. Flowers are odorless except in S. fragrans which produces a somewhat unpleasant, bitter, musk-like scent.

Nectar. — Nectar glands when present ( Table 2 View Table 2 ) are septal, as they are in the entire subfamily Ixioideae ( GOLDBLATT 1990, 1991; GOLDBLATT & MANNING, unpublished). Nectar is secreted from minute, circular pores at the top of the ovary, and flows directly into the base of the perianth tube where it is retained until removed by a foraging insect. In species with the lower part of the tube narrow and tightly enveloping the style ( Table 2 View Table 2 ), a small amount of nectar, too small to measure, is often present in the upper part of the tube, presumably the result of capillary action. No nectar at all was detected in flowers of S. galeata . Measurable quantities of nectar are produced in seven of the 14 species examined for this character ( Table 3 View Table 3 ). In the long-tubed S. metelerkampiae 1.4-3.6 µl of nectar were recorded. Nectar is sucrose rich to sucrose dominant with sugar solute making up 25-38% of the total volume of fluid.

Pollination mechanisms and pollen load analysis. — Pollination varies between Sparaxis species but correlates largely with the mode of floral presentation and nectar secretion. Short-tubed, zygomorphic flowers (group 1) are pollinated primarily by female Anthophora diversipes , which has a large body and a relatively long proboscis 6.5-8 mm long ( GOLDBLATT et al. 1998a). These bees land on the flower and brush both the anthers and stigma lobes as they push their heads into the floral cup. The bees were not observed to scrape or manipulate anthers for pollen. Anthophora diversipes is a polylectic forager ( Table 4 View Table 4 ) and individuals were found to carry the pollen of co-blooming Fabaceae , Lachenalia (Hy a c i n t h a c e a e), Salvia s p. ( Lamiaceae ), Lobostemon (Boraginaceae) , and Iridaceae (including Gladiolus , Hesperantha , Homeria ) in their scopae. The foraging behavior of A.diversipes on Sparaxis species is indistinguishable from the pattern described for bee pollinated Gladiolus species ( GOLDBLATT et al. 1998a), even in apparently nectarless S. galeata . The small flowers of S. parviflora , with exposed anthers, were visited exclusively by worker honey bees ( Apis mellifera ),which actively collected pollen.The presence of hopliine beetles on the flowers of S. caryophyllacea is unexpected and the beetles are most likely only occasional visitors. Sparaxis caryophyllacea shows none of the usual adaptations associated with hopliine beetle pollination.

Tubular flowers (group 2) were either visited by the long-proboscid fly, Prosoeca peringueyi (Nemestrinidae) on Sparaxis metelerkampiae or by Anthophora diversipes on S. variegata . The Prosoeca fly has a proboscis 32-35 mm long ( MANNING & GOLDBLATT 1996) and it forages on the nectar held in the lower part of the perianth tube. These flies grasp the tepals with their tarsi and probe for nectar while continuing to vibrate their wings, contacting anthers and stigmas with the dorsal part of the thorax. Field observations and pollen load analyses show that P. peringueyi individuals visit S. metelerkampiae during the same foraging bouts in which they visit open flowers of Pelargonium magenteum (Geraniaceae) , and species of Iridaceae including Babiana geniculata and Lapeirousia jacquinii ( MANNING & GOLDBLATT 1996) .

Sparaxis bulbifera is visited by a combination of worker honey bees, female halictid and andrenid bees, the tabanid fly, Mesomyia , and the hopliine scarab beetle, Lepithrix ornatella . The remaining species with bowl or salver-shaped flowers produce only traces of nectar and are visited by hopliine beetles and the short-proboscid tabanid fly Philoliche atricornis (proboscis 3–5 mm long) ( Table 4 View Table 4 ). Philoliche atricornis was captured foraging for nectar on S. grandiflora subsp. acutiloba , S. elegans and S. tricolor , and carried either pure loads of Sparaxis pollen or mixed loads of pollen of Sparaxis , Ornithogalum thyrsiflora Jacq. (Hyacinthaceae) , Wurmbea sp. ( Colchicaceae ), and Asteraceae . Beetles appeared to ignore the nectar in the floral tube, but sometimes foraged on pollen, contacting both dehisced anthers and stigma lobes during foraging, copulating, or engaging in agonistic behavior (see GOLDBLATT et al. 1998a). The foetid-smelling flowers of S. fragrans are pollinated by a combination of female halictid bees, worker honey bees, and the scarab beetle Platychelus .

For the two species for which we have not been able to obtain pollination data, we predict, on the basis of floral presentation, that flowers of Sparaxis maculosa are adapted for pollination by hopliine scarab beetles and those of S. roxburghii for pollination by long-proboscid flies.