Separating Searsia refracta from Searsia longispina
This journal post is as a result of a question regarding the differences between the two above mentioned species. Their respective distributions overlap in certain areas and given that they have a similar 'look' in terms of their habit i.e. their architecture, how are you supposed to tell them apart?
A bit of background about S. refracta.....
There are two forms of refracta, the hairy leaved, revolute (leaflet margin folded under), coastal form and the smooth leaved, less revolute, inland form. The coastal form is a species I am familiar with and occurs along the coast and adjacent interior from around Buffalo City (East London) to Gqeberha (Port Elizabeth) with a population around Plettenberg Bay too. I have not yet had the opportunity to see the inland form of refracta in the field, as it occurs a little further north of my immediate area, an area more or less within the block between Makhanda (Grahamstown) - Steytlerville - Graaff Reinet and Nxuba (Cradock).
iNat distribution map for S. refracta
S. refracta distribution map
iNat distribution map for S. longispina
S. longispina distribution map
With regards to longispina, part of its distribution occurs in the same area as the inland form of refracta but also extends down the Sundays and Bushmans River valleys into areas occupied by the hairy coastal form of refracta.
I have only recently had the opportunity to see longispina in the field and have written two journal posts detailing the journey of trying to identify it. These two posts can be found in the links below should anybody be interested.
Chapter 1 - The hunt for Searsia longispina
Chapter 2 - The hunt for Searsia longispina
Before we start.....
Something to bear in mind - there is no substitute for seeing these two species in the field i.e. up close and personal so to speak. Many of us haven't had, and may never have that opportunity though. The differences between the two species described below are the result of many hours poring over the many photos of each species on iNat trying to get a handle on the differences. The descriptions that follow are from my own point of view and, at best, should only be considered as a starting point for anyone trying to get a better handle on ID'ing these two species.
1.0 Fruit
The one thing that is consistent between the two forms of refracta are the drupes (just a fancy term for the type of fruit that Searsia bear)
1.1a Refracta - coastal form drupes
Coastal form drupes 1
Coastal form drupes 2
Coastal form drupes 3
1.1b Refracta - inland form drupes
Inland form drupes 1
Inland form drupes 2
Inland form drupes 3
Both these forms have roundish shaped drupes that start green then develop a pruinose (purplish/blueish) color and then turn light brown/cinnamon color often with a pruinose blush.
Compare these drupe features to longispinas
1.2 Longispina drupes
Longispina drupes 1
Longispina drupes 2
Notice the shape of longispinas drupes - they are flatter on the sides and I guess I would describe their shape as being similar to a peppermint sweet (those hard white ones). Refracta drupes are rounder on all sides. The color of longispinas drupes change from green to light brown without any pruinose blush developing at all.
2.0 Leaf venation
If you are a visual learner like me, you may have noticed there is a difference between the leaves of the inland and coastal forms of refracta, and if it were not for the drupes, you would be excused for assuming that these two forms were two different species. The point of this post is to delve a little deeper into the differences between longispina and the inland form of refracta so I won't be going into any detail into the differences between the two forms of refracta.
Venation pattern is a feature that I have come to use quite often in separating the various Searsia species and is one that is quite useful in separating the two species in question here.
2.1 Longispina leaf venation
The secondary veins give the impression of being neatly arranged along the midrib with fairly even spacing between each secondary, and they tend to fork or branch fairly close to the margin.
Typical longispina leaf venation
2.2 Refracta leaf venation
There are fewer secondary veins per unit lamina (leaf blade) length than for longispina and when the lighting in the photos allows, they are often seen as being offset against each other along the midrib i.e. each secondary arises from a higher/lower point than the one on the opposite side of the midrib. This gives the venation an 'untidier' look than longispina. In addition the veins are impressed i.e. pressed into the lamina creating furrows so to speak, more so than for longispina which, although can have impressed secondary's, it is not a feature that is as obvious as for refracta.
Typical refracta leaf venation
3.0 Bark
Photos don't always provide enough detail of the architecture of the plant and one then has to make a determination based on other small clues. The clues I use when it comes to the features of each species bark and branches follow:
The lower stems of longispina have smoother bark than refracta
3.1 Longispina bark
Typical longispina bark 1
Typical longispina bark 2
3.2 Refracta bark
Typical refracta bark 1
Typical refracta bark 2
Typical refracta bark 3
4.0 Branchlets
The branchlets (the thinner branches near or at the tips) and spines of longispina look rougher and are more obviously striated than for refracta which tends to have smoother, sometimes very finely striate branches, but overall give an impression of being smooth.
4.1 Longispina branchlets and spines
Typical longispina branchlets 1
Typical longispina branchlets 2
Typical longispina branchlets 3
4.2 Refracta branchlets and spines
Typical refracta branchlets 1
Typical refracta branchlets 2
Typical refracta branchlets 3
5.0 Architecture and spurs
The look of the two species is not something that I can define in such a way that a person can look at a single photo and then be able to confidently separate the two - I do not possess that ability! In short, this will require time - lots of it!
Both species have short stout spurs on their older growth and longer spurs on their fresher/newer branches but longispina tends to have much longer, squarrose spurs (squarrose = curves down towards the tip i.e. slightly arched). This feature of longispina is where it's name comes from and is a definitive feature of the species. Refracta on the other hand often has a very spinous look to it due to an abundance of shorter, stout spurs along the branches. A number of spurs often don't have leaves on them or are sparsely foliaged, in contrast to longispina which always seems to have leaves growing on its spurs.
5.1 Refracta spurs
Typical refracta spurs 1
Typical refracta spurs 2
Typical refracta spurs 3
5.2 Longispina spurs
Typical longispina spurs 1
Typical longispina spurs 2
Typical longispina spurs 3
The features described and discussed above hopefully provide a so called 'leg up' for anyone wanting to get to grips with the two species, but unfortunately, there is no short way around this process and time will have to be traded for knowledge.
