Question

Why is the sporophyte of riccia is considered as primitive?

Answer 1

A sporophyte develops from an egg, held within a flask-like archegonium, that has been fertilized and there's more about that process in the SEXUAL 

The fertilized egg grows by the formation of additional cells. In the great majority of species the embryonic sporophyte elongates and one part becomes a foot that penetrates the gametophyte and anchors the embryonic sporophyte to the gametophyte. The opposite end will develop into the spore-bearing capsule (and also the supporting stalk, or seta, in species in which the mature capsule is stalked). The embryonic sporophyte is often protected by a calyptra, a covering that develops from the wall of the archegonium. The calyptra is therefore a very close covering over the embryonic sporophyte