International Symposium on Selection and Breeding of Woody Ornamentals, ISHS Acta Horticulturae Angers, France, 1 December 1992 © Karen Foley 2019
E. pininana from the
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
E. pininana is one of the great Borages which grows on the stony hill
sides and open forests of Laurus azorica in the
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
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
Materials and methods
Seed of E. pininana, collected at the Logan Botanic Gardens,
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 peninsula.
Between 1970 and 1987, meteorological data was collected at Danesfort, Baily,
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
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
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
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
An attempt will also be made to import further samples of seed from the Logan
Botanic Gardens and the
- Anonymous, 1992. Echium. The new Royal Horticultural Society Dictionary of
Gardening. McMillan Press Ltd.
London 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.
Figure 1 - Growth increments of Echium pininana
Flowering and non-flowering plants, 1992
[Copy of original article can be found here.]
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