Luffa Flowers
From a distance they all look the same but they are different.

Flowers on Luffa plants vines contain separate male and female flowers. Due to this phenomenon the flowers are considered imperfect. If the flowers were to contain male and female reproductive systems together on one flower then it would be considered a perfect flower.
Male flowers produce pollen that pollinators transfer to the female flowers to initiate fertilization. Female flowers have an ovary or ovaries and produce eggs that will hopefully be fertilized by male pollen, the flower base will then enlarge to create a fruit. As the fruit develops the flesh becomes the internal protection known as endosperm that provides nourishment as well. Fruit, vegetable and nut skins are known as exocarp — the outer protection. There are exceptions, of course, because sometimes the protective layers combine or are extremely hard.
Did you know that in Culinary Terminology a fruit is sweet tasting plant part? Cucumbers are botanically considered fruits because of there seeds but since they are not sweet they are known as culinary vegetables. In the culinary world Luffas are vegetables.
Let us take a closer look at each flower type.
Female flowers on Luffa plants are always individual.

On the other hand, male flowers are always found in clusters.

After a couple days, the male flowers shrivel up and fall down. Fallen male flowers decompose and provide nutrients to the soil that the plant will intake through the roots by diffusion, and micro-organisms in the soil. I hope this helps Luffa enthusiasts distinguish the different reproductive systems.
