Hakea sericea or Hakea decurrens physocarpa: how did the question arise and how relevant is it?

When I began observing Hakea plants and uploading those observations to iNaturalist, I always identified Hakea plants with terete leaves as Hakea sericea, following the information available at https://invasoras.pt and later https://flora-on.pt where only two Hakea species were mentioned: Hakea sericea with terete leaves and Hakea salicifolia with flat leaves.
To my surprise, many observations of Hakea plants with terete leaves remained unidentified by other users, never reaching Research Grade. At some point I was told that the identity of the Hakea species with terete leaves was being questioned, with several people suggesting that it could be Hakea decurrens physocarpa rather than Hakea sericea.
Worried that this uncertainty could have a negative impact on weed control in Portugal (observations that did not reach Research Grade would not be imported to some databases, affecting the spatial coverage of such databases and any maps produced from them), I tried to learn more about this issue, searching for reliable descriptions of both species and asking for help from Australian and South African naturalists. At some point we seemed to reach a consensus that the Hakea species with terete leaves observed in Portugal is most likely Hakea decurrens physocarpa. Some recent observations, however, suggest that Hakea sericea might be present as well, reopening the question.

Many people have already dedicated tens or hundreds of hours to this issue - but what is the practical relevance of it, regarding weed control?

  • The distinction between Hakea salicifolia and the other two species is absolutely relevant (especially for weed control by volunteers), because
    Hakea salicifolia does not require special precautions (we can walk through a patch of Hakea salicifolia wearing shorts and a T-shirt without being injured), whereas Hakea decurrens and Hakea sericea may cause injuries even when wearing long sleeves, leather gloves and glasses;
    Hakea salicifolia doesn't seem to produce flowers and seeds before 4 years of age (no seed pods seen in Lousã in plants under that age), whereas Hakea sericea and/or Hakea decurrens (whichever species we have in Portugal) apparently produces the first flowers and seeds as soon as 1 year after germination - 3-year-old plants can have hundreds of seeds already.

  • The distinction between Hakea sericea and Hakea decurrens physocarpa does not seem relevant:
    both species are equally hard to remove, requiring special care and equipment;
    both species can produce flowers and seeds at a very early age;
    it is believed that a lignotuber is absent from both species: resprouting after fire was never observed, at least in Lousã.

If we are concerned about weed control and ecosystem preservation - a huge task for which the human resources available are always scarce - perhaps we must be pragmatic and focus on the distinction that is actually relevant: the distinction between the weedy Hakea species with terete leaves (Hakea sericea and/or Hakea decurrens, both in the "Sericea group") and the Hakea species with flat leaves (Hakea salicifolia being the only such species observed in Portugal). If we want to use iNaturalist for that task, encouraging many users to make observations and identifications that can reach Research Grade, then we really should define some taxon that includes Hakea sericea, Hakea decurrens and perhaps other species with terete leaves but excludes Hakea salicifolia. iNaturalist's taxonomy includes the levels "subgenus", "section", and "complex": is there any such taxon that is consensual among botanists and could be used to separate the Hakea species with terete leaves vs flat leaves? This can sound like a petty request from a Portuguese user but it could have practical relevance also for South Africa, New Zealand and perhaps Spain and other countries in the near future.

The efforts to identify the weedy species shall go on, but in the meantime let's make that slight ajustment that would be helpful for the really urgent task: weed control.

Lähettänyt mferreira mferreira, 1. heinäkuuta 2021 09:54


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