Which vegetative part is involved in the Bryophyllum plant and the Begonia plant?

Vegetative propagation is the process of producing a new plant from a plant’s vegetative parts, such as the leaves, stem or roots.
This form of asexual reproduction takes place via the leaves of the Bryophyllum plant. Bryophyllum is a tropical herb featuring broad leaves with notches at its margins. New shoots are formed in shallow notches of the leaf margins. Newly formed plants can detach from the leaves and grow into a full plant after falling on the ground. Bryophyllum is also often referred to as the “air plant” because it can form new shoots when suspended by a piece of string or twine.
Begonias can be propagated using a number of different methods, but the most common way is via seeds, stem cuttings and leaf cuttings.The "leaf cutting" technique is most popular among begonia growers, particularly for the rex and rhizomatous begonia varieties. The Rex begonia (Begonia rex cultorum) uses its leaf veins to create new plantlets, which then root into the soil. A grower can then separate each new plant from the mother leaf and transfer it to a new pot.
https://academic.oup.com/jhered/article-abstract/15/11/463/822134?redirectedFrom=PDF

https://homeguides.sfgate.com/begonias-reproduce-leaves-44889.html

https://www.researchgate.net/publication/283786298_STUDY_ON_THE_VEGETATIVE_PROPAGATION_OF_SOME_BEGONIA_L_SPECIES