A Close-up View of a Hybrid Foamflower

Tiarella cordifolia 'Tiger Stripe'

by Brian Johnston   (Canada)

The Saxifrage Family (Saxifragaceae) of which Foamflower is a member, contains about 700 species.  Tiarella cordifolia has flower stalks covered with delicate, star-shaped flowers sprouting very long stamens.  These stamens are so numerous, that it appears as though the flower-head is surrounded by a yellowish-white cloud – hence the common name Foamflower.  The plant is diminutive, with its multiple flower-heads reaching a maximum height of only 30 centimetres.

Tiarella, the plant’s genus name, comes from the Greek word tiara.  Originally this meant “turban”, a reference to the shape of the plant’s fruit.  (Other sources contend that it was the shape of the flower’s pistil that resembled a turban.)  The species name cordifolia means “heart-leaved”, a reference to the shape of its leaves.  Although the leaves do appear heart-shaped, a better description might be that they resemble rounded maple leaves.  In addition to being called ‘Foamflower’, the species is also referred to as ‘False Miterwort’, ‘Cool wort’ and ‘Heartleaf Foamflower’.

The image above shows a group of Foamflower flower-heads.  Although a flower’s petals are white, its bright yellow anthers, and rust-coloured unopened buds give the flower-head an attractive appearance.

Foamflower is a clump forming perennial which spreads by sending out runners (stolons) to form a colony.  One such colony can be seen in the images that follow.  Notice that young leaves have a coppery colouration that soon transforms into the normal green.

The stem immediately beneath the flower-head is leafless.  Note that as you go up the stem, the distance between the flower stalks decreases, producing a very dense packing of flowers near the flower-head’s tip.

Two bud-stage flower-heads are visible in the image below.  Both are cone-shaped, and both are extremely small at this stage – less than one centimetre in length!

Higher magnification views show individual flower buds.  Each bud is protected by a single whorl of five, pointed sepals which are fused together at the flower’s base.  This whorl of sepals is referred to as the flower’s calyx.  In several buds, it is possible to see between the sepals, and the flowers’ petals are visible.  Strangely, they appear orange, rather than the white of blooming flowers.

In the images that follow, the two bud-stage flower-heads seen earlier have begun to bloom.  The process occurs from bottom to top.

Notice in the image below, that as a bud opens, its sepals change colour to a pale off-white.  It is also apparent that the assumption that the underlying petals were orange was incorrect.  The orange colour is actually the colour of the anthers, not the petals.  Finally, notice the long white pistil that protrudes from the newly opened bud.

Although a mature flower has many white petals, closer examination reveals that the “petals” come in two distinct shapes.  In fact, the broader, shorter ones with little narrowing at their bases, are sepals.  Between each pair of sepals is a longer, narrower structure held by a very thin stalk.  This is an actual petal.  The flower’s whorl of five petals is referred to as the corolla.

Additional views of blooming Foamflower inflorescences follow.

Examination of the opening bud just to the left of centre in the image below, reveals the unusually large size of its yellow-orange anthers compared to the bud itself.

If one of a flower’s sepals is examined under the microscope, its edge is seen to have many bulbous-tipped (glandular) protuberances.

An opening flower can be seen in the two images below.  Notice in the image on the right, that the outer surface of a sepal is covered by the glandular hairs mentioned above.  Also note the pale green, swollen ovary at the flower’s centre.

To begin, each of the flower’s anthers is protected by a yellow-orange, thin membrane.  Eventually, the membrane dries, its surface cracks, and it falls away to reveal the anther’s pollen grains.

Photomicrographs showing membrane covered anthers can be seen below.

If you look carefully at the area just to the right of centre in the image that follows, you will find the very fine tip of the flower’s pistil.  In this species, the broad base of the style narrows to a fine point at the stigma that it supports.

Photomicrographs showing the flower’s stigma can be found below.  Notice that many glandular hairs cover its surface which increase its surface area, and thus aid in the acquiring and retention of pollen grains.

The two photomicrographs that follow show a flower’s ovary.  Notice that it too is covered with glandular hairs.  The surface has been deliberately punctured to allow a view of its contents.  The ellipsoidal structures within the ovary are immature seeds.

Let’s take a closer look at the leaves of the Foamflower plant.  As mentioned earlier, immature leaves have a coppery colour that soon changes to bright green.

Front and back surfaces of a mature leaf can be seen below.  Each leaf has a long stalk, (or is long-petioled), and is broadly heart-shaped, somewhat like a rounded maple leaf.  The back surface of the leaf has many prominent branching veins.

A closer view of these veins reveals that they are covered with fine, soft hairs.

Even the leaf’s upper surface displays hairs, but they are less densely packed here.

Glandular hairs positioned along the edge of the upper surface of a leaf can be seen in the two photomicrographs that follow.

Similar hairs are visible growing from the veins on the leaf’s underside.

Finally, here is an additional assortment of images of this interesting hybrid, Tiarella cordifolia ‘Tiger Stripe’.

Photographic Equipment

The low magnification, (to 1:1), macro-photographs were taken using a 13 megapixel Canon 5D full frame DSLR, using a Canon EF 180 mm 1:3.5 L Macro lens.

A 10 megapixel Canon 40D DSLR, equipped with a specialized high magnification (1x to 5x) Canon macro lens, the MP-E 65 mm 1:2.8, was used to take the remainder of the images.

The photomicrographs were taken using a Leitz SM-Pol microscope (using a dark ground condenser), and the Coolpix 4500.

A Flower Garden of Macroscopic Delights

A complete graphical index of all of my flower articles can be found here.

The Colourful World of Chemical Crystals

A complete graphical index of all of my crystal articles can be found here.

 All comments to the author Brian Johnston are welcomed.

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