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When is a Protea a Tree?
There are many
definitions of a tree. The usual definition includes that plants must be woody and
perennial, usually with a height component (often greater than 2 or 3 m tall), and
with a basal trunk requirement (usually unbranched at the base, and often exceeding a
certain dbh – diameter at breast height – often 100-200 mm). However, any
rigorous criterion for a real tree will probably exclude all proteas, except perhaps for
the largest Sugarbushes and the Beechwoods.
And yet there are certain proteas considered trees that surely do not meet these criteria, whereas other species, not on the National Tree List, certainly do. Taking the Official South African Tree List (opposite) we find, bearing in mind that some 20% of the tree list are "borderline cases":
Brabejum and Faurea are certainly not contentious – all these species are trees. But why no Paranomus? Pa sceptrum-gustavianus, bracteolaris, candicans and tomentosum all meet the criteria as a small tree or large shrub. Few Spiderheads are trees, but Se fucifolia regularly exceeds 3 metres tall with a big basal stem (certainly bigger in height and basal stem than Ls rodolentum, which is on the list). Spatalla and Sorocephulas, as well as Diastella and Vexatorella, contain no species in the tree category. Presumably the Marsh Rose, Or zeyheri does not branch enough to qualify as a tree, even though it may reach 5 m tall with a thick basal trunk. Only Mi arboreus (on later lists) and fimbriifolius are listed as trees, but surely Mi splendidus and saxatile are the same size, although Mi hottentoticus, pauciflorus (reaching 4 m tall) and stokoei may be disqualified as being too spindly.
Which leaves us with the big three.
Some 11 Conebushes out of over 80 are included in the list. These include some rather spindly members. It presumably excludes some resprouters that may exceed 4 m tall in exceptionally old veld (e.g. Ld spissifolium from the Cederberg). If Ld coniferum is included, why not meridianum or galpinii? If Ld ericifolium is included, why not corymbosum? If Ld ericifolium is not too spindly, then how can Ld uliginosum, rourkei or loeriense be excluded? Clearly, there are many borderline cases that cause inconsistencies. Missing species include our new Ld crassulifolium.
Only 5 Pincushions qualify as trees. The inclusion of Ls cuneiforme at first appears ridiculous, but splendid tree-like specimens occur on the Suurberg of the Addo Elephant National Park. And Ls patersonii, which is included, typically grows no larger than Mi saxatilis with which it is associated. Old specimens of Ls praecox, fulgens and erubescens are just as large as the largest Ls patersonii. Ls vestitum in the Wolseley area easily exceeds any Ls patersonii or rodolentum in size. Ls reflexum and formosum are presumably too spindly to qualify as trees, despite being bigger than Ls patersonii.
Some 27 species (one third) of Sugarbushes are included in the list. Presumably Pr compacta is too spindly to qualify as a tree. The inclusion of Pr magnifica seems strange as this is a sprawling shrub, very seldom exceeding 2 m tall. Otherwise, the listing is not too contentious, although Pr welwitschii very seldom even reaches 2 m tall in South Africa.
Proteas on the National Tree list are:
72 Br stellatifolium 72.1 Mi argenteus (Mi arboreus in later lists) 72.2 Mi fimbriifolius 73 Fa galpinii 74 Fa macnaugtonii 75 Fa saligna 76 Fa rochetiana 77 Ld argenteum 78 Ld strobilinum 78.1 Ld conicum 79 Ld discolor 80 Ld ericifolium 81 Ld eucalyptifolium 81.1 Ld nobile 81.2 Ld procerum 81.3 Ld pubescens 82 Ld coniferum 82.1 Ld salicifolium 83 Ls rodolentum 84 Ls conocarpodendron conocarpodendron 84.1 Ls conocarpodendron viridum 84.2 Ls cuneiforme 85 Ls patersonii 85.1 Ls praemorsum 86 Pr nitida 86.1 Pr magnifica 87 Pr caffra 88 Pr comptonii 88.1 Pr curvata 88.2 Pr rupicola 88.3 Pr eximia 89 Pr gaguedi 89.1 Pr glabra 90 Pr lacticolor 90.1 Pr lanceolata 90.2 Pr laurifolia 90.3 Pr aurea 90.4 Pr laetans 90.5 Pr lepidocarpodendron 91 Pr lorifolia 91.1 Pr coronata 93 Pr mundii (Presumably 92 was Pr mellifera - now Pr repens) 93.1 Pr neriifolia 94 Pr obtusifolia 94.1 Pr punctata 94.2 Pr repens 96 Pr roupelliae roupelliae 97 Pr rubropilosa 98 Pr subvestita 98.1 Pr susannae 98.2 Pr welwitschii
In exceptionally old veld many species grow well above their normal heights. Thus Au cancellata near Robertson is currently 3.5 m tall, although perhaps a bit spindly to be a tree, but one fire will reduce these plants to a more typical height range. Should such exceptional plants or situations be used to classify a species as a tree? If you have any ideas of how to consistently classify our proteas, please tell us.
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