There are a few visual cues that you can look for to help determine if a flower is likely to produce nectar or not.

Like Flower shape: Certain flower shapes, such as those with long, narrow tubes, are more likely to produce nectar than flowers with flat or open structures. This is because long-tongued pollinators, such as hummingbirds or moths, are more likely to be able to reach the nectar in flowers with deep tubes.

Color: Many flowers that produce nectar are brightly colored, which can help attract pollinators from a distance. However, this is not always the case, as some flowers with little or no nectar may also be brightly colored to attract pollinators for other reasons, such as pollen.

Scent: Some flowers that produce nectar also emit a sweet scent to help attract pollinators. However, this is not always the case, as some flowers may emit odors that are unpleasant to humans but attractive to certain pollinators.

If you observe a flower closely and do not see any obvious nectar-producing structures, such as a nectary or small droplets of liquid on the surface of the flower, it is likely that the flower does not produce nectar. However, it is also possible that the nectaries may be located in a less visible location, such as at the base of the flower or on the stem.

hi

your question is important as it should also be taken into account that some plant deliver an intracellulary nectar. Coton swab are then of no help.

And as Naira says, there is also extrafloral nectar. And deceptive flowers.

When you say "no nectar in a flower" do you mean "no nectar in a given flower" or "no nectar by the flowers of this species"?

good luch for your thesis Sachin

Thanks much for your comments! Yes I meant "no nectar produced by a given species of flowers".

Cheers!

So the problem will be that of deceptive flowers. Several species of an entomogamous syndrom nut yield no nectar. They often mimic nectar rewarding species, which is tricky.