Prunus munsoniana is here placed in synonymy with Prunus rivularis, greatly expanding the range of the latter compared to its traditional treatment. Descriptions of Prunus munsoniana and Prunus rivularis differ mostly in size of the plants, leaves, and floral structures. As suggested by G. M. Diggs et al. (1999), Prunus munsoniana is simply a larger version of Prunus rivularis[].
The taxonomic history of Prunus is long and complicated, in part due to the economic value of its fruit crops and also the ease with which some species hybridize. Here, Prunus is circumscribed in its broad sense based on the argument that when viewed on a worldwide scale, the morphologic discontinuities among the segregate genera diminish and they overlap with one another. Included here are species that have at times been placed in the genera Amygdalus, Armeniaca, Cerasus, Laurocerasus, Padus, and Persica.
At the species level, Prunus has been the object of the usual combining and splitting common among taxonomists with different philosophies and opinions. In particular, over-reliance on the indument of various vegetative and floral parts has led to the naming of numerous species and infraspecific taxa. Similarly, too much has been made of fruit colour and palatability in naming taxa of Prunus. It is very likely that, as molecular and genetic data are analyzed and, more importantly, correlated with morphological data, circumscriptions will be redrawn and the number of Prunus species will be reduced[].

Common Name: Creek Plum

General Information

Prunus rivularis is a thorny, deciduous shrub or a small tree; it can grow from 1 - 8 metres tall. The plant usually suckers and can form thickets[].
The plant is harvested from the wild for local use as a food and source of materials. It is sometimes cultivated as a fruit crop, there are some named forms, and is also used in breeding programmes.
There is currently insufficient information available to evaluate this species. The plant is classified as 'Data Deficient' in the IUCN Red List of Threatened Species(2013)[].

Known Hazards

The plant (especially the seed and young shoots) contains cyanogenic glycosides, especially amygdalin and prunasin. When injested, these compounds break down in the digestive tract to release cyanide. Used in small quantities in both traditional and conventional medicine, this exceedingly poisonous compound has been shown to stimulate respiration, improve digestion, and promote a sense of well-being[]. It is also claimed by some to be of benefit in the treatment of cancer - though this claim has been largely refuted.
In larger concentrations, however, cyanide can cause gasping, weakness, excitement, pupil dilation, spasms, convulsions, coma and respiratory failure leading to death[].
The fruits and flowers of most members of this genus generally have low or very low concentrations of this toxin, though the seeds and young shoots can contain much higher levels.
The levels of toxin can be detected by the level of bitterness:- for example sweet tasting almond seeds are a major food crop and are often eaten in quantity, whilst bitter tasting almond seeds are used as a flavouring (in marzipan for example) but are not usually eaten on their own.
In general, it can be considered safe to eat any fruit or seed from species in this genus that either have a sweet flavour or are slightly bitter. Great caution should be taken, however, if the flavour is moderately to very bitter[].

Botanical References

, ,

Range

Southern and eastern N. America - Colorado to New Jersey, south to Texas and Georgia

Habitat

Stream banks, roadside thickets, prairie hillsides, borders of woods; at elevations from 200 - 1,000 metres[]. Usualy found on calcareous clay soils or limestone outcrops[].

Properties

Conservation Status	Data Deficient
Edibility Rating
Medicinal Rating
Habit	Deciduous Shrub
Height	2.50 m
Pollinators	Insects
Cultivation Status	Cultivated, Wild

Cultivation Details

This species is not hardy in the colder areas of Britain, it tolerates temperatures down to between -5 and -10°c[].
Thrives in a well-drained moisture-retentive loamy soil[, ]. Prefers some lime in the soil but is likely to become chlorotic if too much lime is present[]. Succeeds in sun or partial shade though it fruits better in a sunny position[, ].
A fast-growing but short-lived species, it can reach flowering and fruiting age within 3 years from seed[]. It is cultivated (as Prunus munsoniana) for its edible fruit in N. America, where there are some named varieties[, , , ]. It has also been hybridized with other species to produce new fruiting cultivars[].
Most members of this genus are shallow-rooted and will produce suckers if the roots are damaged[]. This species suckers freely in the wild, forming quite large thickets[].
Plants in this genus are notably susceptible to honey fungus[].

Edible Uses

Fruit - raw or cooked[]. A plum with an excellent flavour[]. The fruit is usually quite tart and not so well flavoured as Prunus angustifolia[]. The fruit is about 15mm in diameter and contains one large seed[].
The fruit of the form previously known as Prunus munsoniana is thin skinned with a juicy aromatic flesh that is often of good dessert quality[]. It can be eaten out of hand, used in pies, preserves etc or be dried for later use[, , , ]. The globose fruit is usually red, sometimes yellowish orange, with white dots, around 12 - 25mm in diameter with a single, large seed[, ].

Seed - raw or cooked. Do not eat the seed if it is too bitter - see the notes above on toxicity.

Medicinal

Although no specific mention has been seen for this species, all members of the genus contain amygdalin and prunasin, substances which break down in water to form hydrocyanic acid (cyanide or prussic acid). In small amounts this exceedingly poisonous compound stimulates respiration, improves digestion and gives a sense of well-being[].

Other Uses

A green dye can be obtained from the leaves[].
A dark grey to green dye can be obtained from the fruit[].

The plant (as Prunus munsoniana) has been used in plant breeding as rootstock for the improvement of the Myrobalan Plum (Prunus cerasifera)[].

Wood - hard, heavy. Of little commercial value because of its small size[].

Propagation

Seed - requires 2 - 3 months cold stratification and is best sown in a cold frame as soon as it is ripe[]. Sow stored seed in a cold frame as early in the year as possible[]. Protect the seed from mice etc. The seed can be rather slow, sometimes taking 18 months to germinate[]. Prick out the seedlings into individual pots when they are large enough to handle. Grow them on in a greenhouse or cold frame for their first winter and plant them out in late spring or early summer of the following year.
Cuttings of half-ripe wood with a heel, mid summer in a frame[, ].
Softwood cuttings from strongly growing plants in spring to early summer in a frame[].
Layering in spring.