Tag: plant kingdom

Rudimentary seed habit means plants are reproducing sexually by seed but it is not fully developed. For e.g. in Selaginella female gametophytes are retained on the parent sporophytes for different periods. Within the female gametophytes, the development of the zygote into young embryos takes place. This event is a very important step in evolution as a precursor to seed habit. 

Heterosporous pteridophytes (e.g., Selaginella) always produce dioecious gametophytes. A heterosporous life history occurs in some pteridophytes and in all seed plants. It is characterized by morphologically dissimilar spores produced from two types of sporangia: microspores, or male spores, and megaspores (macrospores), or female spores. In pteridophytes, megaspores are typically larger than microspores, but the opposite is true in most seed plants.

Prothallus is the self supporting haploid plant of the gametophytic generation and is concerned with sexual reproduction. Prothallus is generally monoecious and bears sex organs on the ventral side.

In selaginella, the sporangia near the apex of a vertically-held strobilus or along the upper side of a horizontally-held strobilus are darker in color and are oval. These contain many very tiny orange spores, the products of meiosis of several sporocytes. These nearly-microscopic spores are called microspores. This makes their sporangium a microsporangium and the sporophyll a microsporophyll. The microsporangia is yellowish brown in color.

The strobili of Selaginella or spike moss is heterosporous. It bears both microsporangium and megasporangium on the axis of the microsporophyll and megasporophyll respectively. The strobili with the sporophylls arranged look like a spike or a cone.