Progressive sterilization of sporogenous tissue is a fascinating evolutionary trend observed in bryophytes, showcasing a gradual increase in the proportion of sterile cells at the expense of fertile, spore-producing cells within the sporogonium. This trend signifies an adaptation towards more efficient spore dispersal and protection, marking a key step in plant evolution.

In the simplest bryophytes, like Riccia (a liverwort), sterilization is minimal. The sporogonium is a very basic structure, essentially a spherical capsule where nearly all the internal tissue develops into sporogenous cells, which then form spores. Only a single outer layer forms a protective sterile jacket. There's virtually no seta (stalk) or foot.

Moving to more complex liverworts, such as Marchantia or Pellia, we see a slight increase in sterile tissue. Within the capsule, some sporogenous cells differentiate into sterile, hygroscopic structures called elaters, which aid in spore dispersal. A small, ephemeral seta is also present, elevating the capsule slightly.

A significant leap in sterilization is evident in Anthoceros (hornworts). Here, a substantial portion of the sporogenous tissue develops into a central, sterile columella, which provides support and likely aids in nutrient transport. The sporogonium has a well-developed foot embedded in the gametophyte and a continuously growing seta, pushing the capsule upwards. Sporogenous cells form a cylindrical layer around this columella, intermixed with pseudoelaters (simple, sterile structures).

The pinnacle of sterilization in bryophytes is observed in mosses (e.g., Funaria). Their sporogonium is highly differentiated, comprising a prominent foot, a long, rigid seta, and a complex capsule (sporangium). The capsule contains a large central columella, substantial sterile walls with stomata, and often sterile paraphyses. The sporogenous tissue is restricted to a narrow, cylindrical region between the columella and the capsule wall. This extensive sterile tissue provides mechanical support, protects developing spores, and facilitates their efficient release.

This progressive sterilization demonstrates an evolutionary investment in non-reproductive structures that enhance the survival and dispersal success of the fewer, but better-protected, spores.