Ferns exhibit two distinct sporangial types: eusporangiate and leptosporangiate, reflecting their evolutionary paths.

Eusporangiate Sporangia: These are considered primitive. They develop from a group of initial cells, forming a robust, multi-layered sporangial wall. Eusporangia are larger, lack a specialized dehiscence mechanism, and produce many spores (e.g., Psilotum).

Leptosporangiate Sporangia: Characteristic of most modern ferns, these are advanced. They develop from a single initial cell, resulting in a delicate, single-layered sporangial wall. Leptosporangia are smaller, produce a specific, fewer number of spores (e.g., 32 or 64), and possess a specialized annulus (thick-walled cells) for explosive spore dispersal.

Classification of Sori based on Sporangial Development:
Sori are clusters of sporangia on fern fronds, classified by their maturation sequence:

1. Simple Sorus: All sporangia within the cluster develop and mature simultaneously. This would appear as uniform sporangia ready for synchronous spore release.
2. Gradate Sorus: Sporangia develop sequentially, usually oldest at the center or apex and youngest at the periphery or base. This would show sporangia with varying sizes, progressively smaller from the center outwards.
3. Mixed Sorus: The most advanced type. Sporangia of all developmental stages (young, mature, senescent) are irregularly interspersed throughout the cluster, allowing for an extended period of spore release. This would be a random mix of different sized sporangia, indicating varied developmental stages.