Question

Which one of them is not a submerged hydrophyte?
A.Ceratophyllum
B.Utricularia
C.Vallisneria and Hydrilla
D.Lemna

Answer 1

Vascular plants inheriting from remote marine ancestors a multicellular body with unlimited apical growth and a dimorphic life cycle slowly conquered the land and spread themselves over much of the land surface. Yet, despite this flourishing conquest of the land, some angiosperms, most of the herbs and a few pteridophytes, ventured back into fresh-waters and even further,’ to their ancestral habitat, the oceans.

Complete answer: Ceratophyllum- Ceratophyllum is a submerged aquatic. It has a wide ecological tolerance and grows relatively fast. Disturbance of the water body results in increases in growth through changes in nutrient availability but also in faster dispersal around water bodies allowing greater competition with less vigorous species.
Utricularia- is an annual or perennial submerged or free-floating aquatic plant. Rhizoids may be present or absent, they are branched extensively. There are leaves present on the stolons.
Vallisneria and Hydrilla- Hydrilla, a known global species and native to the warm water regions of Asia is a major invasive aquatic plant and one of the most studied submerged vascular plants. The predominance of Hydrilla in the macrophytic communities of infested water bodies is attributed to its mat-forming tendency, the absence of indigenous biological control agents, and the relatively low light levels needed to achieve half-maximal photosynthetic rates
Lemna- Structurally, the Lemnaceae are the simplest of the flowering plants. The plants are not differentiated into stems and leaves; instead, the plants in the family have an undifferentiated leaf-like body commonly referred to as a frond. Fronds floating, 1 or 2-few, coherent in groups, obovate, flat to thickish, margins entire and thin, usually pale green, shining, nearly always with a sharp ridge with white papillae
Hence the correct answer is option is D, Lemna.
Below is the picture of lemna.

Note:
In hydrarch succession that occurs in an aquatic habitat, the series progression is from hydric to mesic. The submerged hydrophytes belong to the transitional community. It goes through many sequential changes to reach the climax. Submerged hydrophytes are those plants that have their roots anchored at the bottom of the lake or pond. Some examples are Hydrilla, Myriophyllum, Utricularia, Ceratophyllum, Vallisneria, etc.