Coleus scutellarioides, commonly known
as coleus, is a species of flowering plant in the family Lamiaceae (the mint
or deadnettle family), native to southeast Asia through to Australia. Typically
growing to 60–75 cm (24–30 in) tall and wide, it is a bushy,
woody-based evergreen perennial, widely grown for the highly decorative variegated leaves
found in cultivated varieties. Another common name is painted nettle, reflecting its relationship to deadnettles (Lamium species), which are in the same family. (True nettles and their
close kin are in the family Urticaceae). The synonyms Coleus blumei, Plectranthus scutellarioides and Solenostemon scutellarioides are also widely used for this species.
Coleus scutellarioides is
an upright annual or short-lived perennial plant. It may be as much
as 1 m (3 ft) tall, with well branched, more-or-less four-sided stems.
Shorter, more trailing forms have sometimes been described as separate species,
under names such as Coleus pumilus or Solenostemon pumilus,
but are all now considered part of the very variable C. scutellarioides.
The species is extremely variable in the colour and shape of the leaves. They
are somewhat fleshy, varying in size from 1.5–10 cm (0.6–3.9 in) long
by 1–6 cm (0.4–2.4 in) wide, generally ovate in shape, and
borne on petioles (stalks) from 0.5–5 cm (0.2–2.0 in) long.
The leaf margin is divided to a variable degree. Hairs are present on both
sides of the leaf.
The inflorescence is borne on the end of a
stem and, like the leaves, is very variable in size; it may be up to 4 cm
(1.6 in) long, with few or many flowers. The calyx is
bell-shaped, initially only 1–2 mm (0.04–0.08 in) long, but
lengthening to 5–7 mm (0.2–0.3 in) when in fruit. The
bluish-purple petals are joined to form a typical two-lipped labiate flower,
8–10 mm (0.3–0.4 in) long. The stamens are joined for about
half their length and are covered by the upper lip of the flower. The fruit is
described as a "nutlet", and is black, about 1 mm (0.04 in)
long.
Pigmentation
The leaves of the wild species may be somewhat variegated, but this has been developed to an extreme degree in cultivated varieties, whose leaves may include one or more shades of green, white, cream, yellow, pink, red, maroon and dark purple. Green coloration is due to the amount of chlorophyll present in the chloroplasts in the leaves. Red, purple, pink, and orange colors are due to anthocyanins – water-soluble, flavonoid biosynthetic pigments, found in the foliage in addition to chlorophyll. The increase in anthocyanin production is accompanied by a decrease in chlorophyll production. The production of anthocyanins and chlorophyll is affected by light levels; the more light is present, the more anthocyanins are produced, with an inverse relationship to the production of chlorophyll. Anthocyanins are created inside the cell and facilitate photosynthesis in leaves that are exposed to very intense or prolonged sunlight by providing protection from damage caused by ultraviolet light. Some coleus cultivars over-produce anthocyanins and under-produce chlorophyll to the extent that optimal growth is prevented.
