The correct option is B Calotropis stem
The intraxylary phloem is situated on the inner side of the vascular bundles. It is located on the periphery of the pith. It is present either in the form of ring or in isolated patches. It forms from the activity of provascular tissues hence, primary in character.
Salvia does not show presence of intraxylary phloem.
Cucurbita stem shows bicollateral vascular bundles which produce outer and inner phloem but intraxylary phloem is absent.
Calotropis stem shows intraxylary phloem in isolated patches on inner side of vascular bundles.
Therefore, the correct answer is option C.