Flower-of-an-hour

Mallow (Malvaceae family):

Hibiscus trionum L.

EPPO code:

HIBTR

Other names:

Venice mallow

Species information

Lifecycle:

Annual.

Propagation:

Reproduces by seed.

Emergence:

Flower-of-an-hour requires warmer soil temperatures to germinate; therefore, it typically emerges in late spring to early summer. Flower-of-an-hour germinates poorly when close to the soil’s surface.

Habitat:

Flower-of-an-hour is common in row crops, waste places and open fields mostly in southern Ontario. It establishes in all types of soil.

Competitiveness:

Little data exists on the competitiveness of this species, but one can assume that its competitiveness is similar to its relative, velvetleaf.

Identification clues

Seedling

Cotyledons:

Orbicular with a very long stalk and prominent veins.

First leaves:

Flower-of-an-hour’s first leaf is circular, flat, and rounded with a wavy margin. Its second leaf looks similar, but with toothed margins.

Mature leaves:

The mature leaves of flower-of-an-hour have an alternate-leaf orientation. They are three-parted, and each division is deeply lobed.

Mature plant

Stems:

In its early stages of growth, flower-of-an-hour’s stem is erect. As it matures, the stem branches out and spreads. Due to the presence of coarse, whisker-like hair, the plant is somewhat fuzzy looking.

Flowers:

Flowers have pale yellow or white petals with purple-brown centres that are 2–4 cm wide. They emerge from a coarsely hairy calyx with prominent purple veins and a ring of hairy bracts. This plant species flowers from July to late autumn.

Seeds:

Kidney- or V-shaped, with a rough surface and brown to grayish black colour, 2 mm long.

Roots:

Taproot.

Often mistaken for

I know it's not Velvetleaf seedling because the leaves of velvetleaf are heart-shaped, whereas flower-of-an-hour has leaves that are lobed and three-parted.