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Isotoma fluviatilis (R.Br.) F.Muell.
Family Lobeliaceae
Common name: Swamp Isotome

Isotoma fluviatilis (R.Br.) F.Muell. APNI*

Description: Prostrate perennial herb, rooting at nodes, often mat-forming, usually pubescent or sometimes glabrous.

Leaves 4–12 mm long, 2–8 mm wide, oblong, elliptic or ± linear or the lower ones ovate or obovate, margins ± entire to crenate or toothed; shortly petiolate or upper leaves sessile.

Flowers solitary, axillary, bisexual or unisexual; peduncles usually 5–30 mm long. Calyx lobes 1–1.5 mm long. Corolla white or pale blue with a deeper blue zone edging yellow near base of lower lobes; tube 2–7 mm long; lobes 2–8 mm long, oblong, almost acute, nearly equal but oblique, the 2 upper lobes separated rather lower down. Anthers ± glabrous, lower 2 each with an apical bristle and several smaller ones. Ovary inferior, obconical, 3–4 mm long in female flowers, <1 mm long in male flowers.

Capsule obconical to obovoid, slightly asymmetric, 3–6 mm long, c. 3 mm diam.


Flower
Photo J. Plaza

Herbarium
Sheet

Herbarium
Sheet

Flowering: late spring to summer.

Distribution and occurrence: Grows in moist sand or mud on edge of streams or seepage areas, in granite areas.
NSW subdivisions: NC, CC, NT, CT, ST, NWS, CWS, SWS, LHI
Other Australian states: Qld Vic. Tas. S.A.
AVH map***

This species is variable, depending on seasonal conditions. It is difficult to satisfactorily separate subspecies australis from subsp. borealis. Further investigations, including cytological examination, may be necessary to distinguish them.

Text by B. Wiecek
Taxon concept:

 Key to the subspecies 
1Flowers unisexual and plants dioecious; corolla 4–7 mm long, inner surface glabrous. Leaves 5–15 mm long. Ovary with short sparse or long dense hairs. Female flowers with corolla 4–6 mm long; anthers small, pale without pollen; ovary 4–5 mm long, ovules fertile. Male flowers with corolla usually 4–7 mm long; anthers blue-black, pollen fertile; stigma rarely exerted from the anther tube, ovary 1–2 mm long, ovules absent or rarely 1 or 2subsp. fluviatilis
Flowers bisexual; corolla 6–15 mm long, inner surface hairy2
2Corolla 6–10 mm long; leaves 5–12 mm long, 2–5 mm broad; pedicels 5–40 mm long in flower, to 60 mm in fruit. Corolla tube and lobes hairy inside. Ovary glabrous or minutely pubescent.subsp. borealis
Corolla 7–15 mm long; leaves 5–13 mm long, 2–7 mm wide; pedicels 3–8 mm long. Corolla blue, rarely pinkish, tube and lobes hairy inside. Ovary mostly glabrous
                       Back to 1
subsp. australis

APNI* Provides a link to the Australian Plant Name Index (hosted by the Australian National Botanic Gardens) for comprehensive bibliographic data
***The AVH map option provides a detailed interactive Australia wide distribution map drawn from collections held by all major Australian herbaria participating in the Australian Virtual Herbarium project.
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