Where should the loss of flagellated sperm be marked on the phylogenetic tree?

Options have not been provided. They are as follows:

a.) At the base of seed plants

b.) Both at the base of angiosperms and at the base of the gnetophytes, pines, and redwoods clade

c.) At the base of the gnetophytes, pines, and redwoods clade

d.) At the base of angiosperms

Answer:

b.) Both at the base of angiosperms and at the base of the gnetophytes, pines, and redwoods clade

Explanation:

The phylogenetic tree of plants was made according to several characteristics. When vascular tissue made entry in the tree, it got divided into seedless vascular plants and seeded vascular plants. Till this time flagellated sperm was observed in plants.

When the seeded vascular plants were further divided into angiosperms and gymnosperms, flagellated sperm was first lost at the base of angiosperms. None of the angiosperms have flagellated sperms. Gymnosperms further got divided into two clades. The clade containing ginko and cycads still retained the flagellated sperm. But the clade consisting of gnetophytes, pines and redwoods lost flagellated sperm. So the characteristic of flagellated sperm was lost again at the base of gnetophytes, pines, and redwoods clade.

Hence, loss of flagellated sperm should be marked on the phylogenetic tree both at the base of angiosperms and at the base of the gnetophytes, pines, and redwoods clade.