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A study on the pollination of Sparaxis (also Iridaceae) by Goldblatt et al. (2000) shows
that a species of Mesomyia Macquart, 1850 (Tabanidae) and the nemestrinid fly
Prosoeca peringueyi Lichtwardt, 1920 both visit flowers with ‘sucrose-dominant’ nectar.
Subsequent work showed that the nectar sugar characteristics in long-proboscid flypollinated
species of Iridaceae, Orchidaceae and Lamiaceae are ‘sucrose-rich or -
dominant’ (Goldblatt & Manning 2000). However, surveyed Pelargonium L’Hér. ex
Aiton species (Geraniaceae), with one exception, have ‘hexose-rich or -dominant’
nectar (Goldblatt & Manning 2000). From such divergent nectar properties, Manning &
Goldblatt (1996) concluded that nectar sugar composition is not a significant factor in
the Prosoeca peringueyi (Nemestrinidae) pollination guild. This observation was
confirmed for other long-proboscid species by Goldblatt & Manning (2000) in their
review on long-proboscid fly pollination in southern Africa.
Data from the current study show that samples of long-tubed Lamiaceae such as P.
reflexus, P. hilliardiae, P. ambiguus, O. tubiformis and S. tubulosa all had truly sucrosedominant
nectar (54 – 96% sucrose), while long-tubed species such as P. saccatus
(long-tubed form) and T. longiflora had truly hexose-dominant nectar (Table 1).
Plectranthus species that are not long-tubed, but that are visited for nectar by the longproboscid
S. wiedemanni (e.g. P. ecklonii, P. ciliatus, P. zuluensis and P. fruticosus) all
have truly sucrose-dominant nectar, as do O. tubiformis and S. tubulosa, that have
been inferred to be visited by this nemestrinid fly species (Potgieter & Edwards 2001).
The sample from the long-tubed I. hypoestiflora (Acanthaceae), which also belongs to
the S. wiedemanni pollination guild, showed equal amounts of sucrose and hexose
(Table 1). While most of the species correspond to a sucrose-dominant pattern, there
are exceptions.
The question then, is whether Plectranthus species that are visited by different types of
pollinator have different nectar classes as a result. Most Plectranthus species recorded
in Table 1 have sucrose-dominant nectar, with P. saccatus and some samples of P.
oertendahlii being the exceptions with hexose-dominant nectar. Plectranthus
oertendahlii is pollinated by medium-proboscid acrocerid flies (see Appendix), but then,
so is P. ciliatus and P. zuluensis T.Cooke, which have sucrose-dominant nectar.
Plectranthus saccatus happens to be the one variable species for which limited
pollinator data was evident during this study: the long-tubed form of P. saccatus is
long-proboscid fly-pollinated and, from garden-based observation, at least one
medium-tubed form is pollinated by S. wiedemanni (see Appendix). A further exception
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