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I am struggling to understand the classification of flowers as hypogynous, perigynous, and epigynous.

The diagram showing in which I have problem

According to my textbook (Biology NCERT Grade 11), diagram (b) is classified as perigynous. However, it seems to me that the ovary is positioned below the other floral parts (since the point of attachment of the ovary to the thalamus is lower than the attachment point of the other floral parts), which would typically categorize it as epigynous.

I am referring to the definition provided in my textbook:

Based on the position of the calyx, corolla, and androecium with respect to the ovary on the thalamus, flowers are described as hypogynous, perigynous, and epigynous. In hypogynous flowers, the gynoecium occupies the highest position, while the other parts are situated below it. The ovary in such flowers is said to be superior, e.g., mustard, china rose, and brinjal. If the gynoecium is situated in the center and the other parts of the flower are located on the rim of the thalamus almost at the same level, the flower is called perigynous. The ovary here is said to be half-inferior, e.g., plum, rose, peach. In epigynous flowers, the margin of the thalamus grows upward, enclosing the ovary completely and fusing with it, while the other parts of the flower arise above the ovary. Thus, the ovary is said to be inferior, as in guava, cucumber, and the ray florets of sunflower.

Could someone clarify the criteria for classifying flowers into these categories and explain how the diagram I’ve provided fits into this classification?

Additionally, I would appreciate if someone could elaborate on the concept of a "half-inferior" ovary in perigynous flowers. Why is it referred to as "half-inferior" and why not "half-superior"?

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It's all related to the position of the female parts of the flower (gynoecium) with respect to the other flower parts.

In A you can see that the ovary sits clearly above the insertion points of the petals, sepals etc. In B and C you can see that these parts are mid-way up the gynoecium, while in D, the ovary is enclosed and below the insertion points of the other parts.

If it helps, the roots of the words offer clues:

  • Gyno: as in epiGYNous or GYNaecologist, means female.
  • Epi: as in EPIcentre (earthquake), means over or upon.
  • Peri: as in PERImeter, means around or about.
  • Hypo: as in HYPOdermic needle, means under.

So, in the word epigynous, the other parts of the flower are over (epi) the female parts (gyno); likewise in the perigynous, the other parts are about (peri) at the same level as the female part.

I'm not sure on the origins of why inferior is used rather than superior; conventions in botany were established quite some time ago. However, there is one possibility: you can only be so superior, but you can have many levels of inferior. Once the ovary is above the petals etc. insertion point it is superior, above all others, and it can't get any more superior. On the other hand, if it is inferior, then it can be partly inferior until it become superior.

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  • $\begingroup$ Sir, thank you very much for taking the time to write this detailed answer. $\endgroup$
    – Madara Uchiha
    Commented Nov 18 at 17:19
  • $\begingroup$ Sir, you mentioned, "Likewise in the perigynous, the other parts are about (peri) at the same level as the female part." Based on this explanation, diagram C appears to fall under the category of perigynous, whereas diagram B does not. Would it be correct to say that the book is mistaken in categorizing the flower shown in diagram B as perigynous? Shouldn't it instead be placed under epigynous? $\endgroup$
    – Madara Uchiha
    Commented Nov 18 at 17:20
  • $\begingroup$ @MadaraUchiha The gynoecium includes all the bits in white (ovary, style and stigma), so B still fits the description. I'll edit my answer to make that more clear. It certainly isn't epigynous as it isn't enclosed. $\endgroup$
    – bob1
    Commented Nov 18 at 19:51
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    $\begingroup$ The terms also relate to where the other tissues connect to the ovary, not simply the vertical position on the diagram. Example b is perigynous because even though the calyx, corolla, and androecium converge at a point above the ovary, they form a combined tissue (hypanthium) that meets up with the ovary on it's lower portion. $\endgroup$
    – Darlingtonia
    Commented Nov 18 at 20:19
  • $\begingroup$ @Darlingtonia, could you please mention the sources where I can find the complete definition of this classification? $\endgroup$
    – Madara Uchiha
    Commented Nov 20 at 4:13

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