Beauty as it resides in the eye of the beholder can be found in absolutely any plant that grows on the earth.  Hate for an invader plant that is ruining someone’s crop or causing trouble of whatever sort, could erase all traces of beauty from the eye of an aggrieved onlooker!  Some may, for example, not find the pink pompom flower (Campuloclinium macrocephalum) currently invading the Gauteng Highveld pretty at all, as it is so scary in its impact on our natural environment. 

Because personal gardening practices and plant usage habits differ, remember: Your weeds and my weeds and our weeds are always three different lists!  Some may recall Herman Charles Bosman’s writing about cultivating blackjacks and kakiebos in his flower garden!  (Kakiebos is of course today a commercial crop in the cosmetics world.)  And every ‘ugly’, unwelcome plant has a natural habitat far away, where it may be admired and does not constitute a problem (like the ugly duckling)! 

What is a weed?  A weed is an unwanted plant that grows where people decide it shouldn’t.  When plants are introduced artificially into areas where their (numbers controlling) natural enemies are absent, their numbers may become uncontrollably high, to the extent that they may invade new areas and displace local or indigenous plants.  Indigenous plant populations require passport control of some sensible kind for itinerant exotics to prevent plant anarchy and plant xenophobia.

The Global Compendium of Weeds (See www.hear.org ) lists 28000 plants ‘watched for their behaviour’ and classifies about 1000 of them as weeds.  It deals with different categories or kinds of weeds, depending on the circumstances of a plant’s appearance in specific terrain, or different reasons for people to find it unacceptable:

Economic weeds interfere with agriculture, horticulture, nurseries and other commercial ventures that are hampered by the appearance of unwelcome and troublesome plants. 

Noxious weeds are plant species identified by the government of a country in its legislation as sufficiently unwanted, negative or detrimental, to enforce eradication and prohibit introduction.  Noxious and economic weeds are often exotic plants introduced either deliberately or by accident, causing extensive and unforeseen harm, hardship and losses hard to combat.

Quarantine weeds are plant species prohibited by law from being brought into a country.

Sleeper weeds have been defined as posing threats in the future to the preferred plant life of a country or specified area; such plants may exist inside the country already in a currently non-detrimental way, or may just have been identified as likely threats without formal proof.

Native weeds are indigenous plants inside or beyond their normal or original areas that have been identified as unwanted due to their negative economic impact or other specified harmful effects. Naturalised species occur in self-sustaining or spreading populations without human interference (as far as is known) and not impacting on the environment in a manner considered negative by people. (Some naturalised species may be sleeper weeds.) Introduced species are any plant species imported for a commercial (or other) purpose.  Such a species may become naturalised or be a sleeper weed.  Many food crop plants, forestry trees, garden plants and other commercial crops fall in this category.  Theoretically plant cultivars and hybrids created locally should be seen as introduced species.  Moving plants within a country to new areas where they have not grown before make them introduced species in their new artificial habitats.  They may on the one extreme become weeds through (usually unexpected) invasive performance, or on the other they could be endangered and lost forever if continually collected in their natural environments and transplanted in unsuitable areas where they die. Garden escape is a horticultural species unintentionally seeding outside gardens, multiplying from abandoned gardens into adjacent areas or growing vegetatively from dumped garden waste into natural environments. Cultivation escape is similar to a garden escape, but starting off from some agricultural or other commercial crop cultivation practice, usually a monoculture. Environmental weeds are species that invade natural ecosystems. Casual aliens are plant species that are introduced into new habitats inadvertently or without human assistance and survive there, appearing occasionally without reaching stable and significant population levels, thus never growing in nuisance value to deserve being classified as weeds. These categories that have been created for understanding and managing specific plants better, serve to indicate the complexity of our botanical environment.  What do we learn from this? 

Alien or foreign plants impact on new natural habitats upon being introduced there.  Should gardening then be allowed at all?  Certainly!  There must be gardens as a key ingredient to human life for many reasons in commercial, lifestyle, spiritual and other directions.  And so many plants have been sufficiently studied and planted for so long that we know much about the many desirable garden subjects with absolutely no invasive habits (and plants that need protection from extinction through being planted in more places).  But being informed, vigilant and connected through our information networks, plant lovers and gardeners should always be careful, law abiding and learning about how to relate to our local plant world wisely, in order to sustain it well.