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B. Nectar Volume and Concentration
Nectar volume ranges for 19 studied taxa are shown in Table 4, arranged according
to corolla tube length and with main nectar-feeding pollinator class indicated. The
highest volume of nectar was found in a flower of the long-tubed form of P. saccatus
(8.7 μl), with the other three long-tubed species of Plectranthus (pollinated by S.
wiedemanni) showing moderate maximum nectar levels (2.4 – 3.2 μl). The beepollinated
P. ernstii, which has a relatively short corolla tube, showed a maximum of
6.8 μl, while the bee-pollinated P. petiolaris E.Mey. ex Benth. had a maximum of 3.2 μl.
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Table 4: Nectar volume range and corolla tube length of 19 species or forms of Plectranthus,
and Py. urticifolia. Pollinator class represents the main nectar-feeding class of pollinators; Apin:
Bee (Apidae, Apinae), Nem: Fly (Nemestrinidae), Acro: Fly (Acroceridae), Tab: Fly (Tabanidae);
Shape of corolla base and presence of spur indicated; Nar: Narrow corolla base, Sac: Saccate
corolla base. Species marked with an asterisk* are visited for nectar by the nemestrinid fly, S.
wiedemanni.
Species Volume
range
(µl)
Floral visitors excluded
n Corolla
tube
length
(mm)
Corolla
base
shape
Pollinator
class
Voucher
P. ambiguus * 0 – 2.7 32 20 – 33 Nar Nem CP 86
P. hilliardiae * 0.2 – 2.4 40 21 – 32 Sac Nem CP 112
P. reflexus * 0.9 – 3.2 8 24 – 30 Sac Nem CP 95
P. saccatus (long) * 1.4 – 8.7 10 20 – 30 Sac Nem CP 120
P. zuluensis (dark)* 0.4 – 1.4 11 10 – 16 Sac Acro CP N12
P. zuluensis (pale)* 0 – 1.1 33 10 – 16 Sac Acro CP 118
P. ecklonii * 0.1 – 1.4 28 10 – 15 Nar Nem, Apin, Tab CP 114
P. saccatus (med.)* 0.1 – 1.8 17 9 – 11 Sac Nem CP 108
P. petiolaris 0 – 3.2 61 7 – 11 Nar Apin CP 115
P. oribiensis 0.2 – 0.6 7 6 – 12
Sac,
Spur
Apin CP 102
P. hadiensis 0 – 2.4 82 6 – 8 Sac Apin, Nem CP 92
P. ciliatus 0.2 – 2.8 25 6 – 8 Sac Acro, Apin CP 116
P. fruticosus * 0.1 – 0.9 23 5 – 8 Sac Nem CP 126
P. saccatus (short) 0.2 – 1.1 24 5 – 7 Sac Acro? / Apin? CP 131
P. ernstii 0.3 – 6.8 25 4 – 8 Sac Apin CP 85
Floral visitors not excluded
Py. urticifolia 0 – 1.4 74 11 Nar Apin CP 1064
P. laxiflorus 0.2 – 1.7 40 10.5 Nar Apin, Nem CP 135
P. oertendahlii 0 – 0.4 33 8 – 13 Sac Acro CP 97
P. petiolaris (pink) 0 – 1.8 31 7 – 11 Nar Apin CP 100
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