This unusual flower is found in Middle and southern Europe.

The plant is bushy with hairy, erect and unbranched stems. Leaves are dark green and lanceolate to narrow elliptic, with a prominent midrib on the underside. (see photo button !L! below)

The Latin name of the species, purpurocaeruleum means purple and blue and refers to the changing colour of the flowers with the progress of flowering.

Flowers are funnel-shaped and carried in a simply branched cluster (raceme).

The fruits are bright white, bead-like capsules, 4–5 millimetres long, with a glossy surface. They are very hard (hence the genus synonym Lithospermum, meaning "stone seed". (see photo button !S! below)

Herbaceous perennial with thick, stocky roots, often growing in dense groups.

Stem covered with short stiff hairs. Leaves large, lanceolate , terminating in a long point. Lower leaves larger and wider, (up to 60 cms in length) with leaf stalks (petioles), upper leaves smaller and narrower (up to 25cm in length), attached directly to stem (sessile).

The petal tube is surrounded by 5 hairy sepals, 1.5–2cm long, fused at the base and narrowly pointed at the tips. A ring of 5 pollen-bearing stamens are joined directly to the inside of the petals near the top of the tube. The flowers produce nectar in glands at the base of the petal tube and pollination is by long tongued insects such as bumble bees. However the female parts of many flowers are sterile and seed capsules relatively rare. This suggests the flower depends to a large extent on vegetative reproduction, producing many plant shoots from a single root stock.

Tuberous comfrey survives well in shady locations such as deciduous woodland. As well as reproducing by seed, it possesses underground stems (rhizomes) that not only store food, enabling it to survive the winters, but also spread outward, colonising the surrounding area and producing numerous young clonal plants as it goes. These young vegetative offspring can be seen particularly well in autumn, their fresh leaves contrasting with the older parent leaves that are already dying back.

Stems are unbranched and softly hairy. Leaves are oval, pointed at the tip and narrowing toward the base with distinctly marked veins. There is a clear reduction in leaf size from top to base of the plant.

The flower tube is surrounded by a ring of 5 finely pointed, hairy sepals, standing outwards with a spiky appearance. The flowers themselves are a subtle pale creamy yellow, the opening of the flower tube less constricted than that of purple comfrey so the floral parts inside are clearly visible, the single long style often seen projecting well beyond the petals. The usual pollinators are various types of wild bees.

This plant is biennial, (flowering in the second year of growth, then dying), or perennial, (lasting several years and flowering each year).

The whole plant is roughly hairy with elongated (lanceolate) leaves.

The flowers start pink and turn vivid blue as they mature. All the stamens protrude and retain their red colour, giving a stark contrast to the bright blue petals. The male parts of the flower mature before the female parts, to avoid self-pollination. The stamens are of different lengths and project beyond the flower. The tip (style) of the female carpel is forked which gives rise to the common names in German (Natterkopf) and English (Viper's Bugloss), being reminiscent of a snake's tongue.

These deep-rooted plants grow in Middle and Southern Europe, favouring warm, dry conditions. Their seeds can survive for long periods in the ground during unfavourable times, germinating when good conditions eventually return.

They have a dense leafy appearance, the basal leaves with silvery spots. (see !W! button below) The petals never open out so flowers appear in bud even when in full bloom. They are pollinated by highly specialised, long-tongued bees. The 2-3mm nut-like seeds drop as soon as they are mature and the plant continues flowering at the same time (flowering and fruiting simultaneously).

This is a herbaceous annual where the young plant may flower in the first season or in the following year, remaining dormant during the winter (winter annual).

The stems are hairy, upright, often thickly branching from the base. The basal leaves are stalked and arise in a rosette from the base of the stem. Their shape narrows towards the base. The upper leaves are smaller and lack stalks, arising directly from the stem. All leaves are covered with soft hairs.

The flowers are pale blue to grey and very small (2 – 5mm diameter). The flower-bearing stem is leafless, becoming longer as the cluster uncurls. The individual flower stalks also lengthen as the fruit capsules develop. At the same time the sepals of the calyx become larger and more hairy, eventually enclosing the developing seed capsules. The seeds are shiny black to dark brown, 1.2 to 2.5cm across with 2 sharp edges.

This is a small annual plant, early flowering with tiny inconspicuous flowers only a few millimetres in diameter.

The stem is upright and lengthens as the leafless flower spike uncoils, successive flowers bloom and the fruit capsules mature.

The hairy fruit capsule is as long as its horizontal stalk and the points of the sepal capsule remain open as the seeds inside develop.

This is a summer or winter annual (either flowering in first season or overwintering to flower in following year). A herbaceous plant with upright stems, occasionally branched from the base which is tinged with red, also sometimes the tips of the leaves.

Leaves and stem are covered with stiff hairs. Leaves are pointed, rarely rounded at the tips.

Flowers are small, the floral disc 3 -4mm diameter, whitish in colour and only slightly longer than the sepals. They produce very little nectar, therefore not often visited by butterflies. Pollinating insects are mainly hoverflies and certain types of bees.

The yellow-brown seeds have a rough warty surface. Dispersal is mainly on the feet of animals.