For some people, any species, which is not native, is by definition invasive. For others, any species which reproduces freely and wanders, so to speak, without control, over-running backyards or forests, such as, Odocoileus virginianus, the white tailed deer, is invasive. This gives rise to the by now familiar misdirected, non-productive assaults on each groups perspective. Each stakeholder has defined the solution differently and thus the definition of the problem is completely unintelligible to each. We have, therefore, the wicked inconvenience of invasive species.
A search on line of invasive Prunus spp. gives, ironically, several native Prunus – americana, serotina, and virginiana, along with the famous tidal basin flowering cherry, Prunus yedoensis. Inherent contradictions abound in the definition of invasive making it difficult to identify those species that may be causing environmental or economic harm, as differentiated from native-only versus exotic anything-goes battle. The latter two of this list are the weeds, yet another term of art – weeds – ,black cherry and chokecherry.
I was able to find Prunus x incamp ‘Okame’, which is a cross between two species outlined below, the following note: “Invasive potential: little, if any, potential at this time”. Emboldened I plunged on finding the same "little potential note" for Prunus sargentii, serrulata, and the Washington favorite, yedoensis. As with politics, all things invasive, are local and though my search shows Prunus subhirtella, the autumn cherry with little potential for invasive habits, local reports from the Potomac gorge seem to suggest a possible problem species.
The tendency to unintentially confuse the initial discussion by using common names such as flowering cherry does nothing to further the discussion. If the solution is to protect natural areas and to encourage self sustaining eco-systems, then some standard of harm needs be applied. If the solution is to recreate to the best of our abilities and resources what we think things looked like a number of years ago, then the over-arching native only definition comes into play.
What are we trying to accomplish? This is the discussion that should be taking place. Are we trying to reintroduce the habitat of the beaver long the Tidal basin? What is the cost of attempting to mitigate the environment to a setting which we think might reflect an age gone by? Who among us believes that they control the group societal definition of beauty? Will this group attempt to legislate their ideals of beauty? Are we proposing to replace the well manicured, ordered, predictable, controlled landscapes of our modern received cultural imperatives with the perceived chaos and disorder against which we as a society have for so long contend?
Because we do not directly debate these, and more, questions, we find no opportunity for consensus, but close our ears to the multitude of stakeholder positions. The flowering cherry is a major economic force in Washington, D.C. Whether it can survive the mounting foot traffic, and perhaps the change in climate is yet to be seen. Watching it from the interface with our natural areas is a normal gardening function. Assessing the damage potential is a continuous part of land management. Establishing thresholds and indicators of invasive tendencies on a system destructive scale is encouraged, but reading on an internet list, and assuming the worse, solves nothing, as does, my search, for it lacks ground truthing. The internet is a great tool, but it is not science.
If we begin to focus in on the cherry tree as invasive, it helps to know of what we are speaking; in other words which cherry tree. When we issue blanket statements which claim a problem, we should at least know of what we speak. Below a list of new world cherries and relatives, copied from “FRUITS FROM AMERICA”. The list of ornamentals from outside of the United States is extensive, and thus cited directly from “Sakura: The Flowering Cherries of Japan” :
Prunus campanulata Maxim. 'Hikanzakura' - this is a small tree with dark black-brown bark and scarlet flowers. The flowers are relatively large and open with numerous, delicate stamens. The peduncles are pendulous, and before fully opening the flowers hang down and appear like bells. picture courtesy: © TopTropicals.comPrunus donarium Sieb. 'Kanzan' - this tree is actually a hybrid of Prunus 
donarium Sieb., P. Lannesiana Sieb., and P. serrulata Lindl. and is therefore sterile with the pistils to two, small, green, leaf-like bodies. It is sometimes classified as a cultivar of these species instead. It is the most common cherry in suburban landscapes with strong upright branches which spread out. It is an erect tree with large rose flowers with numerous petals numbering up to 50. picture courtesy:© 2003; University of Oregon, Eugene OR 97403; (541) 346-1000
donarium Sieb., P. Lannesiana Sieb., and P. serrulata Lindl. and is therefore sterile with the pistils to two, small, green, leaf-like bodies. It is sometimes classified as a cultivar of these species instead. It is the most common cherry in suburban landscapes with strong upright branches which spread out. It is an erect tree with large rose flowers with numerous petals numbering up to 50. picture courtesy:© 2003; University of Oregon, Eugene OR 97403; (541) 346-1000
Prunus incisa Thunb. picture (left)courtesy of: Botany Photo of the Day is a project of the UBC Botanical Garden and Centre for Plant Research, located in Vancouver, British Columbia Canada.
'Fujizakura' (or flowering cherry of Mt. Fuji) This is a delicate tree of medium size with slender branches and very pale pink flowers. The flowers are of medium size with small stamens.
Prunus jamasakura Sieb. picture (below right) courtesy of: aoki2.si.gunma-u.ac.jp/BotanicalGarden/HTMLs/...
'Fujizakura' (or flowering cherry of Mt. Fuji) This is a delicate tree of medium size with slender branches and very pale pink flowers. The flowers are of medium size with small stamens.
Prunus jamasakura Sieb. picture (below right) courtesy of: aoki2.si.gunma-u.ac.jp/BotanicalGarden/HTMLs/...
Giogi-gijozakura' A small tree with ascending branches, grayish bark with rather small, pale tawny to green leaves which are glabrous, obovate or eliptic, glaucescent beneath with long awned teeth and small glands. The flowers are pink with a corolla of 14 petals. The flowers bloom in the middle part of April and are planted at the Gioji Temple, Saga near Kyoto.'Hiyoshizakura' An erect tree with brown-gray bark and reddish leaves which are tawny when young. The flowers are pink and double with a corolla of 28 petals. The flowers are of medium size with a diameter of 3.5 cm. They typically flower in early to mid April. This cultivar is the one planted in the grounds of the Hiyoshi Shrine in Sakamoto, near Otsu, Shiga Prefecture.
'Kotohira' An erect tree with gray-brown bark and green leaves. The flowers are pale pink passing to white with a corolla of 20-25 petals. The cultivar blooms in the middle part of April and is the one planted in the Kotohira Shrine in Kagawa Prefecture.
'Osawazakura' An erect tree with brownish bark and tawny, glabrous leaves which are brownish when unfolding. The flowers are pink with a corolla of 15-18 petals. The cultivar blooms in the latter part of April and was developed by Sano Nursery Garden which is a major center for the production of flowering cherries in Japan.
'Ouchiyama' - An erect tree with gray-brown bark and tawny to green in maturity, glabrous leaves, which are rather thin in texture, and somewhat glaucescent beneath. The flowers are very nearly white, pink when in bud, and have a corolla of 15-20 petals. It flowers in the latter part of April and is the cherry of the Ninnaji Temple near Kyoto.
'Sanozakura' This cultivar is a slightly smaller, erect tree with tawny leaves. The leaves are glabrous, rather small, minutely serrate and glaucescent beneath. The flowers are pale pink and double with 12-15 petals. This cultivar can also be found in the wild around the Sano area.
'Yamazakura' This cultivar is an erect tree with reddish green leaves. The flowers are variable in size with a diameter of 2.5 - 4.0 cm. The flowers have only 5 petals and are a light pink color. The corymbs are 2 flowered. The flowers usually bloom in the first or middle part of April. This is one of the more popular cultivars in Japan and is extensively cultivated in many cities.
An extremely common species and this list represents only a small proportion of important cultivars
'Eigenji' - an erect tree with grayish bark and tawny green leaves which are glabrous, oblong, and slightly glaucous beneath. The flowers are large with a diameter of 5.0 cm and a corolla of 7-11 petals which are a pink-tinged white. The peduncles are unusually elongated and glabrous. These cherries flower in the middle part of April and are planted at the Eigenji Temple in the Shiga Prefecture.
'Fudanzakura' - an erect tree with black brown bark and tawny leaves. The flowers are small to medium sized with a corolla of 5 petals which are pale pink and rather darker in bud. This cultivar is interesting because of the long length and unusual time of flowering. 'Fudanzakura' begins flowering in the latter part of October and continues flowering through the latter part of April of the next year.
'Gyoiko' - an erect tree with brownish bark and tawny leaves. This is one of the more unusual of the Sakura because of its flowers. The flowers are of medium size with 13 petals which reflex when in full flower. It is the color of these petals which is so unusual; the flowers are pale green and partially pale yellow, striated with green lines, and longitudinally striped with red when in full flower. These cherries are a hybrid of P. donarium and are infertile with the pistil reduced to a petaloid structure. These cherries bloom in the latter part of April.
'Kikuzakura' another very unusual cultivar sometimes known as 'Chrysanthemoides' in this country due to the chrysanthemum-like appearance of the flowers. This is an erect tree with dark-brown bark and true green leaves. The flowers are of medium size and with a corolla of 125 pink petals with the inner 80 much smaller and darker in color. The peduncles are elongate, nodding and glabrous. These cherries bloom in the latter part of April.
'Oshimazakura' - an erect rather delicate tree with grayish bark and tawny-green, minutely serrate leaves. The flowers are smaller for this species with a diameter of only 3.7 cm. The corolla consists of only 5 petals which are white with a subtle suffusion of pink. The flowers are more delicate in appearance than most and do not last as long. The peduncles are green and glabrous. The flowers have a distinct, extremely pronounced fragrance which is their most important feature. These cherries bloom in the latter part of April.
'Taoyame' - an erect tree with gray-brown bark and with red tawny, glabrous leaves which are slightly glaucous beneath. The flowers are large and pink in hue with a corolla consisting of 20-25 petals which are rounded, slightly rugose, and convex on the outside. These cherries bloom in the mid to latter part of April and are planted at the Hirano Shrine in Kyoto.
'Eigenji' - an erect tree with grayish bark and tawny green leaves which are glabrous, oblong, and slightly glaucous beneath. The flowers are large with a diameter of 5.0 cm and a corolla of 7-11 petals which are a pink-tinged white. The peduncles are unusually elongated and glabrous. These cherries flower in the middle part of April and are planted at the Eigenji Temple in the Shiga Prefecture.
'Fudanzakura' - an erect tree with black brown bark and tawny leaves. The flowers are small to medium sized with a corolla of 5 petals which are pale pink and rather darker in bud. This cultivar is interesting because of the long length and unusual time of flowering. 'Fudanzakura' begins flowering in the latter part of October and continues flowering through the latter part of April of the next year.
'Gyoiko' - an erect tree with brownish bark and tawny leaves. This is one of the more unusual of the Sakura because of its flowers. The flowers are of medium size with 13 petals which reflex when in full flower. It is the color of these petals which is so unusual; the flowers are pale green and partially pale yellow, striated with green lines, and longitudinally striped with red when in full flower. These cherries are a hybrid of P. donarium and are infertile with the pistil reduced to a petaloid structure. These cherries bloom in the latter part of April.
'Kikuzakura' another very unusual cultivar sometimes known as 'Chrysanthemoides' in this country due to the chrysanthemum-like appearance of the flowers. This is an erect tree with dark-brown bark and true green leaves. The flowers are of medium size and with a corolla of 125 pink petals with the inner 80 much smaller and darker in color. The peduncles are elongate, nodding and glabrous. These cherries bloom in the latter part of April.
'Oshimazakura' - an erect rather delicate tree with grayish bark and tawny-green, minutely serrate leaves. The flowers are smaller for this species with a diameter of only 3.7 cm. The corolla consists of only 5 petals which are white with a subtle suffusion of pink. The flowers are more delicate in appearance than most and do not last as long. The peduncles are green and glabrous. The flowers have a distinct, extremely pronounced fragrance which is their most important feature. These cherries bloom in the latter part of April.
'Taoyame' - an erect tree with gray-brown bark and with red tawny, glabrous leaves which are slightly glaucous beneath. The flowers are large and pink in hue with a corolla consisting of 20-25 petals which are rounded, slightly rugose, and convex on the outside. These cherries bloom in the mid to latter part of April and are planted at the Hirano Shrine in Kyoto.
Prunus nipponica Matsum. picture courtesy of: Copyright © 1995-2007 UC Regents. All rights reserved.
'Chishima-zakura' a shrubby plant with grayish bark and reddish leaves. The corolla consists of 5 petals which are pink and rounded. The peduncles are short green and pilose. This cultivar flowers in the middle part of April.
'Chishima-zakura' a shrubby plant with grayish bark and reddish leaves. The corolla consists of 5 petals which are pink and rounded. The peduncles are short green and pilose. This cultivar flowers in the middle part of April. 
(Note-see P. subhirtella 'Pleno-rosea' on questions of classification) 'Edohigan' - an erect tree with grayish bark and tawny green leaves. The flowers are of medium size with a ameter of about 2.8 cm and a corolla of 5 pink petals. The branches are thinner than most and are covered by the blossoms when in bloom in the latter part of March.'Shidarezakura' a tree with pendulous branches and grayish bark. The leaves are tawny green and serrate. The flowers are small with a diameter of only 2.0 cm and a corolla of 5 pink petals. This tree is very delicate in appearance with its down sweeping branches and simple, pale pink flowers. It blooms in the latter part of March to the first part of April.
'Yae-benishidare' (Pleno-Rosea)- a medium sized tree with pendulous branches and grayish bark. The leaves are tawny-green at first and develop after the flowers. The flowers are medium sized with a diameter of 3.0 cm. With a corolla of 20 deep pink flowers hanging from pendulous, slender, red peduncles. This tree blooms in the first to middle part of April.
'Yaehigan' - an erect tree of medium size with grayish bark. The leaves emerge tawny-green and are serrate. The flowers are of medium size with a diameter of 2.5-3.0 cm and a corolla of 8-10 pink petals. 'Yaehigan' blooms in the first part of April.
Prunus pseudo-cerasus Sieb. no picture
Mountain Cherry This is a wild species of cherry and hence there are no important cultivars. It is used however in breeding and was used in the hybrid in many species including 'Yamazakura' of Prunus Jamasakura. However there are some wild varieties including Higanzakura or equinox cherry, Takane-zakura or peak cherry, and Miyama zakura or deep mountain cherry.
Prunus Sargentii Rehder picture courtesy of: Copyright © 2007 BBG'Ezoyamazakura' - an erect tree with brown bark and reddish bronze foliage. The flowers are single wit 5 very deep pink petals which are darker when in bud. Though a hybrid of Prunus pseudo-cerasus and P. serrulata, this tree is fertile.
Prunus serrulata Lindl. The 'Sato' Cherries
This group of cherries is the most prevalent in the United States and is the most familiar. Some sources in fact incorrectly classify all flowering cherries under this name. Many of the cultivars including most of those covered in this paper are in fact hybrids of this species, however.
'Amanogawa' ('Erecta') - This cherry which is strictly erect and columnar when young, but opens up with age, is ideal for very restricted spaces between buildings. In a garden it is better as a group than singly. The pale pink, large , frilled, semi-double, fragrant flowers open medium late among slightly bronzed leaves which in autumn turn pale yellow and pinkish red.
'Fugenzo' ('James Veitch') - a tree very similar to 'Kanzan' in appearance, but on a lower more spreading crown, with shorter stalked buds of similar flowers, but with redder buds and leaves
'Okiku' - considered by some to be the most beautiful of the flowering cherries, but still little known in the U.S. Strong upright growth is veiled in clusters of frilled, semi-double, green-eyed, pale pink flowers.
'Pink Perfection' - the only cherry not of Japanese origin, this is a cross between 'Shimidsu' and 'Kanzan' raised in 1935 and quite frequently seen in Surrey, its native country. Its flowers are in big hanging bunches and in good years they cover the tree. The flowers open a rich pink and fade to white which adds interest to this tree.
'Shimidsu' - a low crowned, flat topped tree of slow growth but with excellent flowers. Large bunches of flowers hang with a lilac tint beneath similarly colored leaves which become bright green as the flowers open. The flowers are very large, double and white, hanging on long stemmed branches.
'Shirofugen' a variation on 'Shimidsu', flowering at the same time, but lasting longer. It is a taller and more spreading tree and it displays three colors. The buds are a deep pink and beneath the red leaves they open pink for a few days until turning white for a week or more. Thenas the leaves turn green the flowers revert to a pale pink.
'Tai Haku' or Great White Cherry - This cherry was lost in Japan around 1700, but a single tree was found in 1923 planted in a Sussex garden. Collingwood Ingram, who discovered it, raised grafts and every 'Tai Haku' in the world is derived from this plant. Young plants have raised branches and long shoots covered in mid-season by large, single white flowers among red leaves. The leaves are well spaced and leathery and on some trees turning a bright red in autumn.
'Ukon' - the only flowering cherry cultivated which has , pale buff-yellow flowers. They are semi-double, long stalked and below pale brown or khaki leaves. At maturity the flowers turn a pure white with a red eye. The leaves are large and dark , like 'Tai Haku' in size and appearance but predominately oblong.
Prunus Sieboldii (Carr.) Wittm. in Gartenflora 'Naden' - and erect tree with grayish bark and semi-double pink flowers which are globose in bud and which have a corolla of 13 petals. Sometimes fragrant, these cherries bloom in the middle of April. Prunus subhirtella Miq. 
picture (right) courtesy of: Copyright 1996 - 2007 Floridata.com LC
'Jugatsuzakura' ('Autumnalis') - a small tree with dark with tawny leaves. Rather large for this species, the flowers have a diameter of 4.0 cm and a corolla of 10-15 pink or white petals. This tree is remarkable in that it flowers from October through the mid part of April if the winter is mild enough. This cultivar is also one of the few which has bright red, beautifully distinctive autumn foliage.
'Kumagai-zakura' - an erect tree of medium size with brownish bark and tawny green leaves which develop after the flowers and are rather small and glabrate which are thinly pilose and with shorter petioles. The flowers are small with a diameter of 2.0 cm and a corolla of 25 rose colored petals which are narrowed above. This cultivar flowers at the end of March.
'Pendula' ('Pleno-rosea I was unable to determine whether or not this is the same as Prunus pendula or not. They are classified in different places depending on the source. The descriptions of this tree and the species P. Pendula were contained in different sources from different periods of time. The volume in which 'Pendula' was classified as a cultivar rather than a species was newer, but less scientific, than the other.) - an erect tree with gray bark and tawny green young leaves with rather pendulous branches covered in pink flowers. This cultivar is more commonly known as the weeping cherry because of the graceful down sweeping branches which give it a similar appearance to weeping willow. It blooms in the first part of April.
picture (right) courtesy of: Copyright 1996 - 2007 Floridata.com LC'Jugatsuzakura' ('Autumnalis') - a small tree with dark with tawny leaves. Rather large for this species, the flowers have a diameter of 4.0 cm and a corolla of 10-15 pink or white petals. This tree is remarkable in that it flowers from October through the mid part of April if the winter is mild enough. This cultivar is also one of the few which has bright red, beautifully distinctive autumn foliage.
'Kumagai-zakura' - an erect tree of medium size with brownish bark and tawny green leaves which develop after the flowers and are rather small and glabrate which are thinly pilose and with shorter petioles. The flowers are small with a diameter of 2.0 cm and a corolla of 25 rose colored petals which are narrowed above. This cultivar flowers at the end of March.
'Pendula' ('Pleno-rosea I was unable to determine whether or not this is the same as Prunus pendula or not. They are classified in different places depending on the source. The descriptions of this tree and the species P. Pendula were contained in different sources from different periods of time. The volume in which 'Pendula' was classified as a cultivar rather than a species was newer, but less scientific, than the other.) - an erect tree with gray bark and tawny green young leaves with rather pendulous branches covered in pink flowers. This cultivar is more commonly known as the weeping cherry because of the graceful down sweeping branches which give it a similar appearance to weeping willow. It blooms in the first part of April.
Prunus tajimensis Makino no picture
'Shofukuji-shidare' - an erect tree of medium size with pendulous branches and serrate, red-brown leaves. The flowers are of medium size with a diameter of 3.0 cm and a corolla of 35 pink petals. It flowers in the first part of April and is the cultivar of the Shofukuji Temple, Yumara in Hyogo Prefecture.
Prunus verecunda Koehne picture courtesy of: http://aoki2.si.gunma-u.ac.jp/BotanicalGarden/HTMLs/kataokazakura.html'Kasumizakura' - an erect tree with grayish bark and tawny, serrate leaves. The flowers are small and have a corolla of 5 pink petals. The peduncles are about two cm in length green and sparsely pilose. These flowers bloom in the latter part of April.
'Nara-yaezakura' - an erect tree with dark-gray bark and red-tawny serrate leaves. The flowers are rather small and have a corolla of 30 - 40 petals which emerge pink but pale to white at the height of flowering. The peduncles are green and sparsely pilose. This cultivar blooms in the latter part of April through the beginning of May.
'Omuru-mikurumagaeshi' - a small glabrous, shrubby tree branching from near the base with green leaves which are rather thin in texture and paler beneath. The flowers are pink small and double with a corolla of 13 petals. It blooms in the latter part of April and is used as a stock for grafting for the cherry trees planted in the grounds of the Ninnaji Temple near Kyoto
'Nara-yaezakura' - an erect tree with dark-gray bark and red-tawny serrate leaves. The flowers are rather small and have a corolla of 30 - 40 petals which emerge pink but pale to white at the height of flowering. The peduncles are green and sparsely pilose. This cultivar blooms in the latter part of April through the beginning of May.
'Omuru-mikurumagaeshi' - a small glabrous, shrubby tree branching from near the base with green leaves which are rather thin in texture and paler beneath. The flowers are pink small and double with a corolla of 13 petals. It blooms in the latter part of April and is used as a stock for grafting for the cherry trees planted in the grounds of the Ninnaji Temple near Kyoto
Prunus yedoensis Matsum.
picture courtesy of: Copyright 2007 iStock International Inc.
picture courtesy of: Copyright 2007 iStock International Inc. 'Somei-yoshino' - an erect tree with grayish bark and green serrate leaves. The flowers are large with a diameter of 4.5 cm and have a corolla of 5 pink petals which fade to white in full bloom. It flowers in the first part of April.
1 comment:
From some research I did awhile back, it is P. pensylvanica, P. serotina and P. virginia that have become naturalized or invasive in Europe, of the more than 24 American Prunus species that have been introduced there (which includes some plums of course). Prunus serotina is a particular problem, with its habit as a colonizer of recently disturbed habitats.
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