Holly leaves are prickly.   But the leaves of the lower twigs and branches are said to have more prickles than the those higher up the tree.   Ivy (Hedera) has lobed leaves but entire leaves can be found on the projecting branches (which bear flowers and fruits) – again often high up and in the light.

The range in variation in any species can be considerable – thinking about holly, their leaves may vary in :

• The number of spines on a leaf
• The number of spines on each side of the leaf
• The length of the leaf (do longer leaves have more spines?)
• The shape of the leaf
• The ‘greenness’ of the leaf – depending on whether the leaf develops in shade or full sunlight
• The shininess of the leaf - the thickness of the waxy cuticle

The holly tree / shrub itself can vary in sex (male or female trees).

Are the leaves and number of spines the same on male and female holly plants

It can vary in size (from shrub to tree) - height, spread, maturity.

Has the tree been pollarded, grazed by cattle or sheep?

Is it growing in shade or full light?

Holly and Ivy are just two examples of the fluctuations in shape and form of an organism;  the variation that any species can exhibit. It is important to recognise that variation or plasticity is part of the normal range of development, or the variation in the form of a species in relation to different environmental conditions.  Naturalists come to recognise these different ‘habitat’ forms of a species.  There was a tendency in the past to give names to these ‘variations in form’ by calling them varieties or even sub-species.

For years, there have been differences in opinion as to what constitutes a species.  Geneticists tend to define a species in terms of organisms that can interbreed and produce fertile offspring, though this does not work for organisms that are extinct or to those that reproduce asexually!   Taxonomists tend to look at the observable differences between organisms in order to determine species.  The ‘species problem’ or how to define a species has occupied many pages in learned texts and the pens of biologists for many years ; it may be seen as the ‘conflict’ between the need of biologists to categorise and name organisms and the biologists' desire to understand the evolutionary processes that give rise to species.

Difference in shape of ivy leaves.

Perhaps time for a look at your holly or ivy?  If you want to determine the prickliness of a holly leaf - then have a look here