There is a single pantheon in all of Shatterworld. Unlike actual earth history, with one group worshiping the Norse pantheon, another Greek, another Native American, etc..., each with their own creation story, all countries and peoples in Shatterworld believe in the same 7 deities, although different cultures may give them different names. These deities inspired by the Greek Protogenoi, and their domains cover earth, fire, air, water, time, plants, and animal life.
The structure is based upon Greek belief that all things were created of a small set of pure elements. While different philosophers believed in different basic elements, I've settled on Earth, Air, Fire, and Water. I've also added Time as an element, for dramatic effect. All life is made up of a combination of these elements. As such, the deity for each element is revered on their own accord, irrespective of "alignment".
Plant life is composed of all of the elements together, and as such depends on each of the elements. While there may be those who hold the plant kingdom in highest regard, they can not do so without due deference to each of the elements which make up the plant life.
Animal life depends on each of the elements, plus plant life. As such, in many cultures it is considered the most advanced state of being. In Calabria specifically, the god of life (Phenes) was held in highest esteem by the Empire. Any spells concerning healing would certainly appeal to Phenes, as would the turning of undead. Therefore, most clerics and paladins would revere Phenes above all others.
Druids would appeal to both Phenes, as lord of animals, and Phusis, as lord of plants. However, they would also revere the gods of the Elements. Worship is seldom given at the expense of other deities.
A Bard playing a harp to effect a spell could first call upon Phusis and Phenes, as his harp is made of wood, and the strings are made of gut. If there are metal parts, Gaia could be invoked, as metal comes from the earth. The song must be carried through the air, so Aeros could be invoked as well. If the spell were meant to affect flame, then Pyros would be invoked as well. All this could be done in a single phrase, or even mentally. The point is not to bog the game system down in details, but to get players to realize that everyone shares the same basic belief system.
It is also important to consider the mechanics by which spells are accomplished in the game world. There is little difference between cleric and magic user spells. Each essentially commands spirit minions to affect a result. A spell which effects the size of a flame actually appeals to the fire elementals which reside within the flame. A fire summoning spell actually summons a very weak fire elemental. All spells are in effect, summoning and commanding spirits to achieve a result. Basically, invoking the name of a god does not cause that god's direct influence. Rather, servants and minions of that god are called forth to do the spell caster's bidding.
The upshot is that the Gods revealed to man, through the Archons that were sent to the world, the names of these spirits, an how to summon them and command them. Many of these secrets have been lost, and it is up to the spell caster, be it cleric, bard, druid or magic user, to search for records of the old ways to learn new spells.