Hi all,
This is only a preliminary note - I will do something in more detail when I have more time.
Members of the Hakea Sericea Group have been introduced to several parts of the world and have spread and become invasive weeds. There has been a lot of confusion as to what species have become invasive in different parts of the world - and many have just been called Hakea sericea by default.
South Africa
Having looked at many iNaturalist observations, I am fairly certain that the main invasive species of the Group in South Africa are Hakea sericea and Hakea gibbosa. These are generally easy to tell apart, as Hakea sericea leaves are glabrous (or nearly so - may have a few short hairs when very young), whereas H. gibbosa is quite villous (hairy) on the new growth - leaves and stems and it is quite persistent. The only other species that is sometimes confused with these is Hakea drupacea which has divided leaves.
Be that as it may - observers should also keep an eye out for other species that may occur from time to time and not just assume that everything is H. sericea.
There are also species of Hakea from other Groups that have become naturalised and a pest in South Africa - but we are not looking at those here.
Portugal
Again, having looked at many observations, I am fairly certain that most of the records in Portugal are H. decurrens and most likely H. decurrens subsp. physocarpa. Unfortunately - many of the records from Portugal are sterile and are without the key determining features such as flowers and fruit. For many decades - it has been assumed that the invasive species in Portugal was Hakea sericea and many records remain labelled as such - including most of the herbarium specimens. These herbarium specimens need to be critically examined.
The most reliable way to distinguish between the two species is by measuring the flowers. If the pistil (gynoecium) is >8mm long it is H. decurrens - if it is <7.5mm it is H. sericea. There are many other characters that can be used and I will discuss these in another post in the future - but the measurements overlap - especially across the full range of the species. Other characters are often difficult to see on photographs (e.g. the hairs). They may be reliable at each end of the range as being either one or the other - but the overlapping ranges make these characteristics unreliable. It is virtually impossible to identify to species level from the leaves alone. The fruit does show some differences, but again there is overlap. The best thing we can do is measure as many plants as possible as noted on the main project page. In this way, we may be able to make a better determination of the species, and document the range of variation within Portugal and elsewhere around the world. The range of measurements may be less than the total range of measurements that one would get from the full range of the species (including Australia) as the Portugal plants probably arose from one or two provenances in Australia and are unlikely therefore to include the full variational range in the species.
There is one other species in Portugal that has become invasive and a pest - Hakea salicifolia - but we are not considering that here as it does not belong to the Sericea Group - and has flat leaves rather than terete.
Spain
So far, Spain has escaped the Hakea invasion that has been seen in neighbouring Portugal. But this may not always be the case, so people in the whole of the Iberian Peninsular should be vigilant.
New Zealand
New Zealand appears to have three species, viz. Hakea sericea, Hakea decurrens and H. gibbosa as invasive pests. To confirm this, we would like to see many more measurements as stated on the Project's home page. At this stage, it appears that Hakea sericea is more widespread and common than H. decurrens which appears to be confined to one small area on the South Island. But we need to confirm the identifications to be sure.
Like Portugal and South Africa, Hakea salicifolia is also an invasive - but is outside this study.
Australia
In Australia, too there has been confusion as to identifications. Particularly in Victoria, past Floras and many wildflower books, etc. have Hakea sericea as a common species - but more recent research has determined that that species does not occur in Victoria (except as garden escapes or naturalised around old settlements or homesteads) and that what was previously called H. sericea is really Hakea decurrens. But there is often more confusion, as two other species (in different Groups but with terete leaves) are often confused with these - Hakea microcarpa and Hakea nodosa. One problem, is that people don't always update their reference books, so I encourage them to use the resources listed below.
In New South Wales, it is even more confusing as there are a number of terete leaved species that get confused. These include Hakea sericea - perhaps the most common and widespread species, - and Hakea decurrens. Other species such as Hakea microcarpa, H. teretifolia and Hakea gibbosa are quite widespread and without good material (flowers, fruits and new growth) are difficult to tell apart. New South Wales also has a number of species with restricted ranges, and these too are difficult to tell apart without flowers and fruit or sometimes, the new growth and have often been just been called H. sericea by default. These include Hakea lissosperma, H. macreana, H. constablei and H. actites within this group, as well as other terete-leaved species such as H. propinqua, H. pachyphylla, and H. bakeriana.
Hybridisation
There has been some discussion as to the likelihood of hybridisation between especially H. sericea and H. decurrens. Although hybridisation is not uncommon in other genera of the Proteaceae, hybridisation in Hakea is not common. There is no record that I can find of hybridisation between these two species
Lignotubers
Many texts state that Hakea decurrens has lignotubers and H. sericea doesn't. More recent research, however has shown that populations of Hakea decurrens subsp. physocarpa in the Grampian Mountains in Victoria don't have lignotubers, and my studies in the Brisbane Ranges show that those too do not have lignotubers. Apparently there is no evidence of resprouting in Portugal which would indicate that lignotubers are not present in those populations and may give a clue as to where the Potuguese populations arose.
Future taxonomy
Many of the Hakea species are difficult to tell apart, and there is still confusion as to the delineation between H. sericea and H. decurrens and its subspecies. I have heard, informally, that someone is beginning a DNA study of these groups - As good as this may be, I am sure it is still some time before we will have more definitive results.
Resources
There are a number of good resources, but the ones I have found the best are:
- Barker RM, Haegi L, Barker WR (1999). Hakea in Flora of Australia Vol. 17B Proteaceae 3. Hakea to Dryandra. pp. 53-64. Melbourne: ABRS/CSIRO. https://www.environment.gov.au/system/files/pages/6d8c5c3b-8545-437e-b9b3-944ac95ee07a/files/flora-australia-17b-proteaceae-3-hakea-dryandra.pdf
- Barker RM & Haegi L. (1996). Hakea in Walsh NG & Entwistle TJ (eds) Flora of Victoria Vol. 3. Dicotyledons Winteraceae to Myrtaceae. Melbourne. Inkata Press. (Updated by Stajsic 2018-03-15) https://vicflora.rbg.vic.gov.au/flora/taxon/d09bbd2a-b739-4646-9ff9-c3c12d2c1f9d
- Barker RM, Harden GJ, Haegi L, Barker WR. (1999) PlantNet NSW. https://plantnet.rbgsyd.nsw.gov.au/cgi-bin/NSWfl.pl?page=nswfl&lvl=gn&name=Hakea
- Barker WR (1996). Novelties and Taxonomic Notes relating to Hakea sect. Hakea (Proteaceae), mainly of Eastern Australia. J. Adelaide Bot. Gard. 17:177-209. https://data.environment.sa.gov.au/Content/Publications/JABG17P177_Barker.pdf#search=Hakea%20%20.
- Lucid Australia Fact Sheets. Hakea decurrens ssp. physocarpa. http://www.flora.sa.gov.au/efsa/lucid/Hakea/key/Australian%20Hakea%20species/Media/Html/Hakea_decurrens_ssp._physocarpa.htm
- Lucid Australia Fact Sheets. Hakea sericea. http://www.flora.sa.gov.au/efsa/lucid/Hakea/key/Australian%20Hakea%20species/Media/Html/Hakea_sericea.htm
I encourage you all to keep a ruler in your back pocket when you go into the field, and if you can - please try and take a close up photo of the flowers showing - where possible - the hairs on the rhachis and pedicel.
