Pelargonium betulinum flower

The petals of Pelargonium betulinum in picture are not always white as seen here. The markings, petal size and shape, as well as all other plant features may vary. Collectively they remain the key to plant identification, by retaining some distinctive cluster of attributes to continue as a species. Propagation within the species is key to this. Symbiotic relations with other species would constitute a reason why a species would need to be recognised by some service providing foreign neighbours. Science can ascertain species identity today by inspection of the DNA. 

Older species may have expanded and compounded the range of their individual differences to justify the recognition of forms, variations, subspecies and eventual splitting of species within the genus. Such differences become more over time, especially where species occur in large distribution areas with much variation in growing conditions. Speciation characterises all living things that perpetuate themselves through offspring amidst environmental challenges to survival. 

The complexity of life forms can also be glimpsed within the individual specimen. The allure of flowering plants being a special case of this phenomenon. Note for instance how colour and form of the petal markings change here between the base and higher up on the upper petal pair. It is pink lower down with straight lines, dark purple with branched and angled lines higher up. Also note how the sepals around the corolla tube are narrow and hairy, attenuating to sharp tips.