A <flower> is an <angiosperm>'s reproductive structure. \x[Stamens]{magic} produce <pollen>; <carpels> enclose <ovules>. <Petals> and <sepals> surround these organs in a complete <flower>, but some <flowers> lack one or more groups, including either reproductive group.<Biology 2e by Mary Ann Clark and others>[Biology 2e, §32.1 Flower Structure, Figures 32.3–32.4: organs and incomplete flowers]{ref}

\Image[/flower-organs-and-enclosed-ovules.png]
{title=<Flower> organs and the enclosure of <ovules>}
{description=Original schematic cutaway of a <flower> with both reproductive groups. Colors separate functions; shapes, organ counts and relative sizes are illustrative. The enlarged <ovule> belongs inside the <ovary (botany)>, not on the <stigma (botany)>. The sketch is not a universal arrangement.}

Read the drawing from outside inward, then trace two routes: where <pollen> is released, and where an <ovule> is enclosed. This reveals why catching <pollen> and forming a <seed> require different structures. A detached <petal> cannot substitute for a <stigma (botany)> simply because both belong to the same <flower>.


 Flower (source code)