The host plant from which amarbel or Cuscuta derives nutrients is commonly known as the "dodder" plant. Dodder is a parasitic plant that belongs to the genus Cuscuta, and it lacks chlorophyll, which is essential for photosynthesis. As a result, dodder relies on other plants, known as host plants, to obtain the necessary nutrients for its survival and growth.

The Dodder Plant:
Dodder plants are thin, yellow or orange-colored, leafless vines that twine around their host plants. They have specialized structures called haustoria, which penetrate the host plant's tissues to extract water and nutrients. Unlike typical plants, dodder plants do not have roots in the soil. They entirely depend on their host plants for sustenance.

Identification of Host Plants:
Dodder plants are opportunistic parasites and can infest a wide range of host plants, including vegetables, crops, and ornamental plants. The identification of host plants is crucial in understanding the impact of dodder infestation and implementing appropriate control measures.

Mode of Nutrient Extraction:
When a dodder plant encounters a suitable host plant, it starts to coil around it using tendrils. The haustoria of the dodder plant then penetrate the host plant's stem, leaves, or other parts, forming connections with the host's vascular system. Through these connections, the dodder plant extracts water, minerals, and other nutrients directly from the host plant's tissues.

Impact on Host Plants:
The presence of dodder on a host plant can have detrimental effects. Since dodder competes with the host plant for nutrients, it weakens the host and hampers its growth and productivity. The haustoria of the dodder plant can also cause physical damage to the host plant's tissues, making it susceptible to infections by other pathogens.

Control and Prevention:
Controlling dodder infestation can be challenging as it has no effective chemical control methods. However, several cultural practices can help in managing dodder. These include removing infected plants, preventing the spread of dodder seeds, and using weed-free seeds or transplants. Crop rotation and tillage practices can also help disrupt the life cycle of dodder and reduce its impact.

In conclusion, amarbel or Cuscuta is a parasitic plant that derives nutrients from its host plant. Dodder, the common name for Cuscuta, lacks chlorophyll and relies on its host plant to extract water and nutrients through specialized structures called haustoria. Identifying host plants is crucial for understanding dodder infestation, and controlling its spread can be achieved through cultural practices and preventive measures.