Question

Which of the following has a haplontic life cycle?
A. Wheat
B. Funaria
C. Polytrichum
D. Ustilago

Answer 1

Plants throughout this life cycle are haploid. In the haplontic life cycle. The gametangium of the gametophytic plant is where the haploid gametes grow. Then two haploid gametes are united to create a zygote, which enters the diploid stage of the life cycle, also known as the sporophytic phase. The zygotes are meiotically split into haploid (n) zoospores during germination, which are then grown into haploid plants. The gametophyte (haploid) stage is the next step.

Complete answer:
Let us look at each of the options to find the correct answer.
Option:A – Wheat is a diploid plant and does not show haplontic life cycle.
Thus, Option:A is not correct.
Option:B - Funaria has a haplo-diplontic kind of life cycle. A free-living haploid gametophyte alternates with a semi parasitic diploid sporogonium during the life cycle (Sporophyte).
Thus, Option:B is not correct.
Option:C – Polytrichum is diploid in nature and shows diplontic life cycle.
Thus, Option:C is not correct.
Option:D – Ustilago is a genus of over $200$ smut fungus that live as parasites on grasses and it has a haplontic life cycle. The haploid stage of the haplontic life cycle is multicellular, while the diploid stage is single cellular.
Thus, Option:D is correct.

Therefore, option D.Ustilago is the correct answer

Note:
Smut fungus belong to the genus Ustilago. Smuts get their name from their black spores, which look like soot or smut. Grain, such as wheat, is replaced by spore masses. It's a parasite that can live on its own. Its different species infect grass ovaries, causing a black powdery clump of spores to form. Because all Ustilago species complete their life cycle on the host, they are classified as autoecious parasites.