E. pininana from the
Canary Islands is a highly decorative sub-shrub that
grows well in mild coastal areas of
. It is valued for its single spike of blue, purple or rose flowers which can
grow from over 1 m to a height of 6 m between February and early June. The
plant flowers in its second or third year and, being monocarpic, dies after
E. pininana is cross pollinated and produces seeds prolifically (in
excess of 200,000/plant), which germinate readily and dense carpets of Echium
seedlings are commonplace. Plants developing from these seedlings survive most
winters but, in some years, a proportion is killed by cold; on two occasions
during the last 17 years all plants were killed by low temperatures of -6 C in
January. After these severe winters new seedlings develop from the seed bank in
It seems possible that natural selection from cold stress will, over time,
produce a more cold hardy strain of E. pininana,, better adapted to
. This hypothesis is being tested.
E. pininana is one of the great Borages which grows on the stony hill
sides and open forests of Laurus azorica in the
Canary Islands . There it is an endangered species
through loss of habitat to agriculture. However, it is naturalised in some mild
coastal areas of
, where it is highly regarded as a striking and beautiful ornamental plant.
It is valued for many qualities. It grows rapidly and, in the vegetative
state, makes a round dome of large textured leaves with good architectural
qualities. In the second or third year from germination the plant will start the
flowering process. Usually robust plants that have grown well and are around 1.5
m tall in the early winter will flower during the following year. This does not
always occur and plants may remain vegetative for a further year. Occasionally
small plants will send up a weak flowering shoot.
When E. pininana flowers normally, it produces a tall slender spire; this
may, on occasions, be 7 m or more in height and is often taller than in its
native habitat. Plants of E. pininana usually produce a single
massive spike of light blue, rose or purple flowers on scorpioid cymes. Although
individual flowers do not last long, the plants remain in bloom from late April
to October because of the large numbers of flowers that are produced
successionally during the season. Being monocarpic, E. pininana, dies
The greatest disadvantage of E. pininana, is that it is not completely
and, even in mild areas, is liable to be killed in an exceptionally severe
winter. It is also very difficult to grow at all away from milder coastal
E. pininana is cross pollinated and produces seeds prolifically, which
germinate readily. This echium forms hybrids easily with some other species,
such as E. wildprettii. (Anonymous 1992). Within stands of E. pininana,
there is considerable variation among plants, both in the colour of the flowers
(blue to purple) and in the maximum height of the plant when fully grown
(usually 2m to over 6m). Because of genetic variation within the population of
, it may be possible to produce a hardier strain through natural selection.
Materials and methods
Seed of E. pininana, collected at the Logan Botanic Gardens,
by Colonel David Price, Kilmokea, Co. Wexford in 1975 was sown under glass at
Kinsealy Research Centre,
in a peat compost. Three pot-grown seedlings were planted in the open at
Earlscliffe, Baily, Co.
(Latitude 53.4 N) in September 1975.
The soil at Earlscliffe, derived from Cambrian shale and quartzite,is a clay
to silty clay loam, well drained with approximately 12% coarse sand, 30% fine
sand, 47% silt and 28% clay in the 0 - 100 mm layer. The natural pH of the soil
is between 5 and 5.5 and the organic matter content around 4.5% in the top 75
The three echium plants overwintered successfully, flowered in 1977 and
produced many self-sown seedlings in 1978. As a result of natural seeding, E.
pininana is now well established throughout all parts of the garden at
Earlscliffe, in other gardens in the locality and on waste ground on the Howth
Between 1970 and 1987, meteorological data was collected at Danesfort, Baily,
about 400 m due north of Earlscliffe. Lowest air minimum temperatures were
also recorded at Earlscliffe, throughout the test period. Records were
also kept of years of total or substantial elimination of the Echium population
as a result of low winter temperatures.
Growth increments of two 2-year-old plants, similar in size and growth habit,
and both 1.4 m high on December 1991, were measured periodically up until
June 14, 1992 .
Meteorological data show that the lowest annual minimum temperature occurred
mainly in the period January to March and varied from -1.7 to -6.0 C. The lowest
temperature (-6.0 C) was recorded on the night of
31 December 1978/1 January
1979 and again on 13/14 January 1987. January was usually the coldest month each
year with an average temperature of +5.6 C.
Highest maximum temperature occurred usually in July or August and ranged
from 22 to 27.5 C. Average annual rainfall was approximately 650 mm spread
over all months.
Of the two plants where growth increments were recorded, one plant flowered
in 1992 and the other remained vegetative. The growth pattern of both plants is
shown in Figure I. The vegetative plant increased slightly in height between
December and early March. From then on, stem growth thickened considerably, but
plant height remained unchanged.
In contrast, the plant that flowered in 1992 increased rapidly in height from
early February onwards and grew particularly rapidly (around 50 mm/day) between
late April and mid May. The rate of upward growth slowed markedly in mid June.
E scorpioid cymes each with
up to 19 branchlets and each bearing 20 to 30 flowers over the 6 month flowering
season. Each flower produces up to 4 seeds and so a medium-sized plant may carry
well over 200,000 seeds. During the late autumn and early winter the seeds are
scattered widely by wind.
After the first plants flowered, dense stands of Echium seedlings were
commonplace in open situations, over 100 seedlings per 100 mm square often being
recorded. In such dense stands only the most vigorous of the seedlings survived,
the others being killed by inter-plant competition.
Self-sown seedlings of E. pininana were generally hardy and were
unchecked by most winters. However, on the two occasions during the last 17
years (1978/9 and 1986/7) when temperatures fell to -6 C, all seedlings and one
and two year old plants were killed. These low temperatures had, however, little
or no effect on dormant seeds in the soil for after both of these severe winters
there was a strong flush of new seedlings in the spring from the seed bank in
In some other years, a proportion only of the seedlings were killed; for
example, in 1985/86 approximately 1/3 of the seedlings were killed, 1/3 had
their growing points damaged and 1/3 survived uninjured. Plants which
survived with damaged growing points subsequently produced two or more flowering
shoots. After these moderately severe winters, the seed bank in the soil
was augmented with seeds from the surviving, presumably hardier, plants.
Figure 1 shows the remarkable speed of growth of E. pininana, in its
flowering year. Some plants can grow from a height of between 1 and 2 m to over
6 m between February and mid June. Growth increments of 40 to 50 mm/day are not
uncommon during this period. Growth slows down rapidly in mid June, presumably
when the plant begins to devote more of its resources to seed production.
Plant loss from low temperatures during the winter is well known in many
fruit, vegetable and ornamental crops. Breeding programmes, involving both
conventional breeding methods and cell hybridization techniques are in progress
in many countries aimed at preventing or reducing damage from low temperatures.
These programmes are concerned mainly with crops of economic importance and much
less work has been done on ornamental crops because financial returns from such
work would generally be low.
In the past, natural selection from cold stress on seedling populations of
fruit and vegetable crops, played an important role in crop improvement. For
tree fruit varieties such as McIntosh apple and Lambert sweet cherry were
products of natural selection and remain among the most important cultivars
because of their superior hardiness (Quamme, 1987). Allowing the local
climate to select out improved plants from large populations is a very
inexpensive method of crop improvement.
Because of the large numbers of seeds of E. pininana, involved in this
study, it seems possible that natural selection from cold stress will, over
time, produce a more cold hardy strain better adapted to conditions in
To test this hypothesis, seedlings from the populations at Earlscliffe are
being distributed to colder locations in
, such as
, where previous plantings of E. pininana, have not survived.
An attempt will also be made to import further samples of seed from the Logan
Botanic Gardens and the
Canary Islandsso that the hardiness of the 'Earlscliffe' strain can be compared with
plants raised from the imported seed.
Anonymous, 1992. Echium. The new Royal Horticultural Society Dictionary of
Gardening. McMillan Press Ltd.
Basingstoke . Vol 2, D-K, 140.
Quamme, H.A., 1987. Low temperature stress in Canadian horticultural
production - an overview. Canadian J. Plant Sci. 67:1135-1149.