A Prelude to Spring - Blackthorn versus Cherry Plum

With spring just about around the corner, one of the great issues of the season among budding botanists is sorting out Blackthorn (Prunus spinosa) from Cherry Plum (Prunus cerasifera). The two are both common hedgerow plants throughout much of lowland Britain and on first look are remarkably similar. The issue seems to have been further compounded by a failure by some books in the past to include Cherry Plum, so it is often off the radar so to speak when people are considering identifications.

The photos below cover the salient identification points in turn, with particular reference to spring features. Blackthorn is a native species, found commonly throughout most of the UK. It is a suckering shrub that is a dominant component of natural, successional scrub and often forms extensive stands with Hawthorn, spreading to form impenetrable thickets if left to grow naturally. Blackthorn tolerates pruning readily and is consequently a very common plant in hedgerows, both as a naturally-occurring native and where planted. The plants are strongly spiny on suckering shoots and long growths, but typically less so on flowering stems.Blackthorn fruits are known as Sloes and are famously astringent and not for the faint-hearted! Although they are well-known as a component of Sloe Gin.

Cherry Plum is a thornless, introduced species that grows as a native in south-east Europe and Asia Minor. Despite being non-native, it is abundant throughout much of lowland Britain, although more so in the south and east. It has been extensively planted for hedging but, unlike Blackthorn, it does not tend to form suckering thickets but instead will grow into a small to medium-sized tree with a good trunk if left unpruned. Cherry Plum fruits are commonly eaten, though they can be a little tart and are better if cooked. The fruits are more commonly eaten on the continent and are often known as Mirabelles (although that name is also given to a small-fruited form of Common Plum (Prunus domestica).

Precise flowering times vary across the country, becoming progressively later as one heads northward. However, Cherry Plum typically peaks about a month earlier than Blackthorn, though with both species having individuals that flower early or late and drawing out the season such that there is a little overlap in flowering times, typically in late March or early April, depending on location.

Typical roadside Blackthorn thicket in flower. Note that even short sucker-growths will produce a few flowers close to the ground (Photo: April 15th).

Slightly closer view of Blackthorn in flower. Note the dense abundance of flowers along the stems, as well as the flowers close to the ground on suckering shoots (Photo: April 18th).

A typical Cherry Plum in an untended hedgerow. When maintained as a hedge, the two species grow rather similarly, but left uncut, Cherry Plum forms a good-sized trunk with only a few suckers around the base (Photo March 14th).

Blackthorn bushes flower prolifically when at their peak in April, with the flowers densely crowding the stems on relatively short flower stalks (photo: April 18th).

A closer view of Blackthorn flowers. Compared with Cherry Plum, the flowers of this species tend to be a little smaller, slightly narrower-petalled and with more prominent stamens, but there is a certain amount of variation in these features (Photo: April 18th).

Cherry Plums are a little less floriferous than Blackthorn, with the flowers mostly borne singly and on relatively longer flower stalks, so thus being a little more spaced apart Cherry Plum flowers typically open with the first leaves (April 13th). 

The stems of Blackthorn typically have very short, downy hairs on them. They are only a little shiny (perhaps because of the hairs) and they are grey-brown or purplish-grey in colour.

The stems of Cherry Plum are distinctly green-tinged, hairless and shiny. In sunny positions, the stems may become purple above, but will usually by green on the shadier underside. Note, however, that pink-flowered cultivars have dark purple stems.

The fruits of Blackthorn are known as sloes and are remarkably astringent! They are dark blue-black in colour and covered with a whitish bloom (this bloom is also found on plums and grapes and is known as 'pruinescence'; a word taken from the genus name Prunus).

Cherry Plum fruits are larger than those of Blackthorn and are sometimes known as Mirabelles (although this name is also used for a small-fruited variety of Common Plum). The fruits may be either yellow, or dark red, with each tree only producing one or other colour. Cherry Plums have a tendency to be biannual croppers, producing a heavy crop only every other year. They typically have slightly longer stalks than sloes which can help to give them a cherry-like appearance.

Forms of Cherry Plum in cultivation often have pink flowers and dull, reddish-purple leaves. They are very commonly planted as street trees in towns and cities and have dark purple fruits. This photo shows the cultivated variety 'Pissardii' which has pink buds opening to very pale pink flowers with a slightly deeper pink centre.

The cultivated form 'Nigra' of Cherry Plum has deeper pink flowers but is generally not as common as the form 'Pissardii'.

Conifers On My Mind

Conifers have been occupying my website time of late and I've finally got the bulk of the East Anglian species up onto Flora of East Anglia now. I may still add more at a later stage, since quite a few of the cultivated varieties can look very different to their original parent species and can cause a lot of confusion. It has been a slow process getting the conifer photos sorted, not least because at an early stage I used Lynford Arboretum as a source of material, before it became very obvious to me that so many of the plants there are incorrectly labelled! I always think that an arboretum with misidentified trees is worse than one with no labels at all, since an absence of labels at least prompts one to get the books out! The Abies species in particular got me tied up in knots and I am sure I will re-visit that group at some point!

We do very poorly in the UK for conifers, with just three native species in the entire country! However, a long history of plant discovery and collection around the world has left us a heritage of magnificent trees to enjoy, many of which show up as self-seeded individuals or long-established plants in public spaces. This impressive specimen of Grecian Fir (Abies cephalonica) can be seen in Earlham Road Cemetery, Norwich.

On the Flora of East Anglia website, I've tried to make sure that usable features for identifying plants are employed; some books use the cones as the main identification feature for the Silver Firs (Abies species) which is rather daft, since the cones not only break apart on the tree (making measurements extremely difficult to achieve) but they also typically only appear at the very top of very tall specimens! This piece of Noble Fir (Abies procera) from the top of a felled specimen at Felbrigg Hall illustrates the point nicely!

I put this photo in as a reminder that the wonderful spring 'flowers' of our larch trees are not too far away now - more on them another time!