When posting images of a plant it is HELPFUL that an indication is given as to whether the specimen was growing in the wild or cultivated.  Just because a plant is not in a park, garden or field is not alone an indication of whether it is a NATIVE species.  Some introduced species become
naturalised and it can be difficult to tell they are not ‘wild’ or not, particularly if the photographer is not familiar with genera typically cultivated as crops or ornamental purposes.
It is of significance whether a plant occurs naturally.  Much is talked about CONSERVATION. It makes sense to concentrate our concerns about NATIVE species and NOT introductions.  Some of the most eye- catching plants may well be INTRODUCTIONS – unfortunately, some are INVASIVE and troublesome. 
Where I live (and thus most frequently botanize) has MANY Alien plant species.
Where I live in the UK is within the old county of Buckinghamshire (nowadays the newish boundary puts me in Berkshire). For recording purposes of The Botanical Society of Britain & Ireland (BSBI) I remain in ‘Buckinghamshire’.  I have a copy of the ‘Flora of Buckinghamshire’ from 1926; it is fascinating to compare the abundance (or not) of species then with nowadays – there have been many changes during the past century.  The same no doubt applies in India.  Collet’s ‘Flora Simlensis’ (1921) allows a comparison with present day Shimla and surrounding areas.
There is not an up-to-date Flora for Buckinghamshire but the useful ‘A CHECKLIST OF THE PLANTS OF BUCKINGHAMSHIRE’  Maycock & Woods (2005) is available.
In it they include, in alphabetical order by genus and species, both NATIVE and ALIEN taxa. ‘Native’ taxa are those believed to be in Buckinghamshire entirely due to natural processes.  ‘Alien’ taxa are those that have been introduced to Buckinghamshire by human activity (intentionally or accidentally).  Those long established in Great Britain (i.e. before 1500) are known as ARCHAEOPHYTES; those established since 1500 are NEOPHYTES.  Other aliens are listed as ‘Casual’ if they do not maintain themselves in the county by seed or vegetative means, or are
obviously planted.
Why 1500?  The first of four voyages across the Atlantic by Italian Explorer Christopher Columbus took place in 1492 and led to the introduction of plant material.  The Romans introduced quite a number of plants into Great Britain. 


Very interesting and informative.


List of invasive alien species of India is available at following link:
http://www.bsienvis.nic.in/Database/Invasive_Alien_species_15896.aspx
Though, we still do not have a list of flowering plants of India !


Thanks for drawing my attention to this LIST OF INVASIVE SPECIES, which I shall check-with and no doubt refer to, from time-to-time.
I shall no doubt question SOME of the identifications!
In light about my post covering Primula malacoides and other ‘naturalised’ exotic species,
I immediately raise a question about the SINGLE entry under Opuntia. The authors have O.stricta Haw. but NOT the common O.monacantha Haw. – which is illustrated and described in ‘Flowers of the Himalaya’.
Stewart lists both in his Catalogue covering Pakistan & Kashmir. O.monocantha being cultivated as far west as the Indus and ascending to
1200m. Naturalised in Sind. 
Whereas he only has O.stricta from Sind and Lahore brick kiln mounds (according to Parker – so a century old record).
I am uncertain what constitutes INVASIVE as opposed to NATURALISED but whatever the PRECISE definition (and there needs to be one), I am surprised that O.stricta should be classified as such UNLESS this species has become INVASIVE in recent decades?
I see both species have entries in eFI (not attempted to verify the identifications) and both are accepted names in ‘The Plant List’ – though other authorities might not agree and no doubt revisions will take place from time-to-time.
Certainly quite a number of species recognised within this genus – so imagine not easy to distinguish between all of them.
I wonder how authors of the list of ‘Invasive’ species in India distinguished between O.monocantha and O.stricta?


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