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Streptocarpus ’Constant Nymph’ and
Its Mutants
It appears that the Arnold Arboretum has introduced to
American gardeners what may turn out to be the most exciting
group of new house and greenhouse plants for a long time. It
all started with a gift of a few plants of Streptocarpus ’Constant
Nymph’ to Dr. Richard A. Howard. Director of the Arboretum,
from the greenhouses at Dunbarton Oaks some years ago.
The potentials of this cultivar as a remarkable house plant became obvious very quickly. It propagates with speed and ease
and its magnificent blue flowers are produced in abundance
throughout almost the whole year. It fully justifies its name.
We cannot take credit for introducing ’Constant Nymph’ in
America but apparently we are responsible for introducing its
five remarkable new mutants, ’Blue Nymph’, ’Cobalt Nymph’,
’Mini Nymph’, ’Netta Nymph’ and ’Purple Nymph’.
To avoid future confusion, it seems wise to get the story
in print. Dr. W. J. C. Lawrence, while working on color inheritance in plants at the John Innes Horticultural Institution in
England in the 1940’s, crossed a particularly good hybrid streptocarpus called ’Merton Blue’ with Streptocarpus ~ohannis. One
of the seedlings of this cross was named ’Constant Nymph’.
Under normal house conditions it will bloom continuously from
April to November. With supplementary lighting it can be kept
in flower all year around.
The unfortunate name, Streptocarpus, can be quickly dismissed as being no more than a description of the ripened seed
pod. It means "twisted fruit". This genus of predominantly
African plants has interested both gardeners and scientists for
a long time for different reasons.
Several unusual characteristics appear in many of the members of the genus. ’Constant
Nymph’ illustrates some of them. There appears to be no true
stem or conventional growing point to the plant. The leaves
seem to grow from the upper surfaces of the bases of other
leaves. The flowers appear to arise from the upper surfaces
of the petioles. As a house plant it can suffer considerable
abuse and survive. If water is deliberately withheld from one
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Streptocarpus
’Constant
Nymph’.
Photo: R. Spurr.
plants for as long as a month, turgor is restored to the
dead-appearing, limp leaves in a matter of hours after watering.
Since ’Constant Nymph’ and its mutants do not come true
from seed, they must be propagated vegetatively. Leaf cuttings are the most effective method for as many as 100 new
plants may be obtained from one leaf Two main methods of
preparing the leaves are used. The leaf blade may be cut
crosswise into several pieces. The proximal ends are then inserted into a rooting medium. Or the leaf blade may be split
down the middle the long way, removing the main vein and
placing the two large pieces of the leaf blade with the long
cut edge in the rooting medium. A great many plantlets will
of these
result from either method A temperature of around 70-75 degrees F seems optimal for rooting. Roots should appear in
about two weeks. In another two weeks independent leaflets
appear which eventually grow into small plants. Progeny should
not be separated from the old leaf until each plantlet has roots
developed at the base of its own leaves. When all the new
plants are eventually removed from the old leaf, these leaf
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sections may be replaced in the rooting medium and another
batch will develop.
It is sometimes possible to get even a third batch of plantlets
but with reduced results. The basal portion of the leaf from
which the flowers arise, should not be left on during rooting.
If this is not removed, roots will appear on this area and flowers
usually develop without the formation of new plantlets. Not
remo"ing this part at the base of the leaf is the main reason
some leaves do not propagate well. Fertilizing nutrients should
not be included in the rooting medium because excessive activity results in producing an abundance of flowers. The result is a heavily-flowered, single-leaved plant with few plantlets.
In March, 1969, the writer was fortunate in being able to
spend about a week in the Netherlands. He was additionally
fortunate in having a close friend, Dr. Robert Legro, as host
during much of this time. During visits to the horticultural experimental station at Wageningen which involved nearly two
days, some time was spent with Dr. C. Broertjes at the Institute
for Atomic Sciences in Agriculture. He was doing experimental
work involving radiation on several kinds of plants. One of
the plants was ’Constant Nymph’. Dr. Broertjes explained a
remarkable characteristic of this plant as well as some of its
relatives which made them particularly valuable as experimental material. When he radiated whole mature leaves, each
new plantlet that developed arose from a single mutated leaf
cell. The resulting entire plant possessed the mutated trait or
traits and could be readily propagated. The troublesome problem of chimaeras common in other plants treated in this manner was eliminated.
In his preliminary experiments, Dr. Broertjes produced 1,650
mutants. Five of these eventually received Certificates of Merit
in the spring of 1969 and are the named mutants with which
we are concerned.
In August, 1969, we requested from Dr. Broertjes propagation material of whatever mutants he cared to release. The
first shipment consisted of unrooted leaves. Due to a delay
enroute almost all arrived in a deplorable state of decay. We
received a second shipment on November 3, 1969. These were
leaves in excellent condition with well developed plantlets attached. They included the previously mentioned mutants In
the greenhouse at the Case Estates all the plantlets had flowered
by May 1970. ’Blue Nymph’ has light blue flowers with a small
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pale greenish-yellow blotch in the throat; ’Cobalt Nymph’ has
intensely dark blue flowers with a small greenish-yellow throatblotch. This tetraploid has a compact habit of growth and flowers of heavy substance. It seems to be more difficult to propagate than the others. ’Mini Nymph’ has flowers very much like
’Constant Nymph’ with a yellow throat blotch. It is very freeflowering and makes a fine compact plant. ’Netta Nymph’ has
dark blue flowers with distinctive darker reticulate venation on
the petals It is also very free-flowering. ’Purple Nymph’ with
its rich purple flowers and small yellow throat blotch seems to
make the largest plants and be the most vigorous of the five.
The response of the general public to these new cultivars can
best be described as covetous. On "Friends of The Arnold Arboretum Days" when a mixture of excess Arnold Arboretum
plant material is sometimes offered free to Friends, the streptocarpus plants are always the first to be taken.
The September/October 1970 issue of The Gloxinian featured
a striking color plate of ’Netta Nymph’ on its cover. This issue
contained an article, "New Streptocarpus Varieties" by Dr. Carl
D. Clayburg. He reviewed Dr. Broertje’s work, described the
new mutants in some detail and mentioned that the Arnold
Arboretum of Harvard University was growing them and
planned to release some propagative material soon to commercial growers. The Kartuz Greenhouses in Wilmington, Massachusetts had already received propagative material from the
Arboretum before the article appeared. Additional leaves were
sent to Wyrtzen Exotic Plants in Floral Park, New York and the
L. Easterbrook Greenhouses in Butler, Ohio.
On June 9th, 1970 we had been given full freedom by Dr.
de Zeeuw, Director of the Institute for Atomic Sciences in Agriculture at Wageningen, to do with these mutants as we wished.
Dr. Broertjes stated that "they are not covered by any kind of
protection; the only thing we did was to have them registered
and commercialized." Recently, when the question arose as
to whether or not the Arnold Arboretum had actually been first
to introduce these mutants to American gardeners, Dr. Broertjes
responded in a letter dated June 22, 1972 saying that, "so far
as I know
we did not send leaves to other persons or institutions
in the United States of America."
There is more to come, for developments have not yet ended.
A white flowered spontaneous mutant has occurred known as
’Maassen’s White’. From this cultivar by use of irradiation and
colchicine a number of mutants and tetraploids have been pro-
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duced. We have been promised propagative material of ’Maassen’s White’. We will hope for propagative material of two
other cultivars that are expected to be released in 1973. One
is a "mini-white type" and the other a white which is described
as a tetraploid with very large flowers.
GEORGE H. PRIDE
References
Broertjes, Cornelis.
Euphytica 18:
Broertjes,
Cornelis.
1969. Mutation
333-339.
Personal
Breeding
of
Streptocarpus.
correspondence.
Varieties.
The Glox-
Clayburg, Carl D. 1970. New
inian 20(5): 19-20.
Streptocarpus
Marston, Margaret E. 1964-65
The Morphology of a Streptocarpus
From Leaf Cuttings. Scientific
and Its
Horticulture 17:
Hybrid
Regeneration
114-120.