The genus Ceratostigma comprises about eight species widely
distributed in China, the Himalayas, Abyssinia, and Somalia. Only three species
are in general garden cultivation, Ceratostigma griff-thii,Ceratostigma
plumbaginoides, and Ceratostigma willmottianum. The species C. plumbaginoides
is best known and most widely cultivated, but it is not a true plumbago,
although it is often offered for sale under the name Plumbago larpentae. The
genus Ceratostigma is distinguishable from the genus Plumbago by various
botanical characteristics not easily recognizable to the average gardener. The
most obvious difference is in the inflorescence: plumbago's has the form of a
terminal spike, while ceratostigma's has the form of an axillary or dense terminal
cluster of beautiful intense-blue flowers.
Ceratostigmas were introduced to the Continent by way of
Great Britain. Alice M. Coats not unjustifiably called it "a lady's
genus" because the story of its success in the West is linked with the
name of a woman. In 1831 the botanist Dr. Alexander von Bunge collected a
ceratostigma in the vicinity of Peking. Thirteen years later, also from Peking,
Robert Fortune sent seed to England, but for some unknown reason the first
attempts at raising the plants failed. Perhaps the seeds did not germinate or
the plants did not survive. In 1846, a certain Mr. Smith sent a specimen from
Shanghai to -Sir George Larpent. It was accompanied by the following message:
"Mr. Fortune attempted to grow this plant but was not successful;
therefore yours is the only specimen in England. It is also rare in Shanghai
and I found it on the city walls. It is one of the most beautiful and most
decorative plants I have seen in China." Considering the tone of this
letter, Sir George evidently felt a considerable responsibility towards the
plant and consigned it to the care of his wife, Lady Larpent. It thrived and
the following year bloomed profusely in their garden at Roehampton in England.
When at first ceratostigma was classified in the genus
Plumbago, it was called Plumbago larpentae in honour of Lady Larpent. Lady
Larpent, however, was not destined to enjoy her triumph for long, for soon
afterwards Sir W. Jackson Hooker was obliged to rename it because of several
"almost insignificant peculiarities" in its structure. He called it
Valoradia plumbaginoides. However, it was renamed once again, this time as
Ceratostigma, the name originally given to it by von Bunge. This name is
derived from the Greek keras (horn) and stigma, because of the horn-like
appearance of the stigma excrescences. By the 1850s, the plant was considered
"common" in English gardens, certain testimony of its rapid rise to
fame.
Cultivation.
Ceratostigmas will thrive in any normal good garden soil, although they have a
preference for a loamy, sandy texture with a percentage of peat or some other
organic material. The position should not be excessively sunny semi-shady in
the south and preferably with a moist atmosphere. In colder areas in northern
localities, a light mulch of dead leaves, straw, or salt hay should be applied
in winter.
Propagation from seed is not necessary in the case of
Ceratostigma plumbaginoides because the spreading, mat-forming habit of the
plant lends itself so well to division in spring. If very large specimens are
desired, the plants should not be disturbed for at least three years. They
should be cut back almost to ground level in spring and given a top dressing of
equal proportions of ordinary garden soil, leafsoil, and peat.
Ceratostigma griffithii C. B. Clarke
Native to northern India, Bhutan, and the Yunnan province of
China. A semi-shrubby, much-branched dwarf bush with a spreading habit.
Evergreen, with small opaque-green leaves margined reddish purple; young
growths very hairy. The flowering period is long, from mid-summer until late
autumn. Intensely sky-blue flowers. Hardy in all except the coldest zones and
suitable for small beds, borders, and for carpeting the soil surface.
Ceratostigma plumbaginoides Bunge
Native to China. Herbaceous perennial with slender, much-
branched, spreading stems that produce upright lateral growths up to high,
although sometimes much shorter. These upright growths are angular, striped
with violet-red, and produced in tufts. Leaves alternate, bright green, obovate, with a line of fine hairs along the
margins. The flowers are borne in small dense terminal groups; gentian-blue in
colour, becoming violet with age, each with a violet-red calyx. Late- flowering
but prolonged from August until the first frost. Not always an easy plant
initially and must have a porous soil; but once established it develops rapidly
and extensively and demands no special treatment. Apart from its value for
small beds, edging, and carpeting, it is an excellent subject for planting in
walls, where the blue flowers make a delightful contrast against the stone. It
has been reputed to dislike alkaline (calcareous) soils, but my own personal
experience has proved this to be untrue.
Ceratostigma willmottianum Stapf.
Native to western China. Discovered by E. H. Wilson in the
semiarid regions of the valley of the Min River in western Szechwan province;
introduced into England in 1908. Of the original seeds sent, only two
germinated and grew, thanks to the care of that great gardener Miss Ellen
Willmott, in whose honour the species was named. It is believed that all
subsequent plants cultivated in Great Britain have originated from these two
plants. This particular species is semi-shrubby in habit with rhomboid foliage
acuminate at the base; densely hairy on the undersurface and bearing large
marginal hairs along the edges of the leaf blade. Flowers are of an intense
blue, borne in tufts, but opening only one or two at a time, thus giving a long
flowering period.
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