Difference between Cactus and Succulents

Cacti vs Succulents:

I like cactus (Plural: Cacti) and succulents so much that I started collecting many cactus types and succulents in my terrace garden. The count increases in number every time I visit a nursery garden.

I always thought that the cactus are the ones with spines whereas the succulents are of the softer, fleshier ones with no spines. I actually believed that this is what distinguishes them both from being a cactus or a succulent. Everything changed after I started collecting the cacti and succulents as I had to know about each plant and its characteristics (of course after I bought them). I did a small research and I came to know about few things:

• All Cacti are Succulents. But not all Succulents are Cacti.
• Cacti and succulents are not distinguished by the spines. But by the presence of  areoles. All cacti have these areoles. But not succulents. Areoles are a white cotton like fluffy part (usually tiny) from which spines or glochids (group  of  hair like spines) or flowers or branches will grow from. 
• Some of Euphorbia species and Agave have spines which make them look like cacti, but they are not, because they don’t have any areoles. So they fall into succulents category.
• The similarities are both cactus and succulents have the ability to retain water for dry and hot environments.
• In cactus, the leaves are modified as spines to conserve water. Cactus store water in their stems and these stems perform photosynthesis, giving them the energy they need. Usually these cactus stems are enlarged to make them store water. These spines trap the moisture within these stems and prevents transpiration (evaporation of water from the leaves) by forming a thin moisture layer near the surface of the stems.
• In cactus, the leaves are modified as spines to conserve water. These spines trap the moisture within these stems and prevents transpiration (evaporation of water from the leaves).
• In Cactus, spines protect these plants from animals and also from us.
• Succulents store water in various part of their body like leaves, stems or roots. These are not deep rooted always near to the surface to absorb any tiny bit of water they get due to short showers or even due. The storage of water makes them look like swollen, thick and fleshy plants. Similar to cactus, stems perform photosynthesis. The presence of less or reduced number of stomata (tiny pores on the leaves) reduce water loss due to transpiration.

Some of the Cactus Photos:

Some of the Succulents: