Synonyms: Hypsela APNI*
Description: Annual or perennial herbs with milky sap, erect or creeping, rhizomatous, much branched, minutely pubescent or glabrous, with a distinct taproot, but sometimes with adventitious roots along the branches.
Leaves alternate, toothed or variously lobed, rarely entire, often petiolate at the base and becoming sessile on the branches.
Flowers solitary and axillary, or in terminal racemes, bisexual or unisexual and then plants dioecious, pedunculate with leaf-like bracts. Calyx shortly tubular, lobed. Corolla only slightly zygomorphic, ± notched anteriorly and with almost subequal lobes spreading horizontally, very shortly and obliquely campanulate at the base, lower 3 lobes often with distinct markings. Stamens fused to the corolla above the middle or near the summit of the tube; lower anthers smaller, with a bristle and a tuft of apical hairs, upper 3 anthers slightly longer and at the apex ± curved down onto the lower ones; filaments fused above, anthers fused around the style. Ovary inferior or semi-inferior, 2-locular, slender style topped by a slightly swollen, more or less hairy and scarcely 2-lobed stigma.
Fruit an urn shaped or conical capsule, 2-valved, loculicidally dehiscent within the calyx lobes, seeds numerous, minute.
Distribution and occurrence: World: c. 12 species, Australia & New Zealand. Australia: c. 10 species (endemic), all States.
Some species suspected of poisoning livestock, but are reported to have an acrid, bitter taste, and be unpalatable to stock. Australiasian species of Hypsela as In Flora of NSW Vol. 3 are now included under Isotoma.
Text by B. Wiecek; key updated L. Murray (Sep 2018)
Taxon concept:
| | Key to the species | |
| 1 | Prostrate creeping or mat-forming perennial herb, rooting at nodes; leaves 1.5–12 mm long | 2 |
| Erect or ascending annual or perennial herbs, leaves usually much more than 15 mm | 3 |
| 2 | Leaves 4–12 mm long; corolla white or pale blue with a deeper blue with yellow edging at the base; capsule 3–6 mm long | Isotoma fluviatilis |
| Leaves 1.5–8 mm long; corolla white sometimes tinged with mauve; capsule 1.5–3 mm long
Back to 1 | Isotoma tridens |
| 3 | Leaves with margins entire, toothed or lobed and lobes cut less than halfway to midrib | 4 |
| 3 | Leaves sessile, linear or narrow-lanceolate, margins entire or slightly toothed, 0.5–3.5 cm long, 1–3 mm wide; corolla less than 20 mm long | Isotoma armstrongii |
| Leaves deeply divided with lobes cut more than halfway to midrib, pinnatifid or pinnatisect
Back to 3 | 5 |
| Lower leaves petiolate, sessile above, oblanceolate to elliptic, margins toothed or irregularly lobed less than halfway to midrib, 1.5–7.5 cm long, 5–55 mm wide; corolla more than 20 mm long
Back to 3 | Isotoma petraea |
| 5 | Leaves 6–10 cm long, 0.5–5 cm wide, pinnatisect with undivided part of lamina 1–2 mm wide, lobes 0.5–2 mm wide, linear, acute, sometimes with a few small teeth | Isotoma anethifolia |
| Leaves 1.5–15 cm long, 0.5–5 cm wide, pinnatifid to more or less pinnatisect with undivided part of lamina usually 3–5 mm wide, lobes 0.3–3 mm wide, more or less linear, acute, margins often again toothed
Back to 4 | Isotoma axillaris |
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