I found a Zohar (Bereishis, Hashmatos) which says that a king wished to plant nine male trees in his garden which were all palm trees. However, he realized that they could not exist without a female, so he planted an Esrog tree among them. The Zohar proves that Esrog is female from the Pasuk which says "Pri Etz Hadar Kapos Temarim." It seems that the Zohar is learning that the Pri Etz Hadar (Esrog) is Kapos to the Temarim (Kapos means hands?).

This is the only source which might help understand the Gemara you mentioned.

מָשָׁל לְמָה הַדָּבָר דּוֹמֶה? לְמֶלֶךְ שֶׁעָלָה בְּלִבּוֹ לִטַּע בְּגַנּוֹ תִּשְׁעָה אִילָנוֹת זְכָרִים, וְהָיוּ כֻלָּם דְּקָלִים. אָמַר, כְּשֶׁיִּהְיוּ כֻלָּם מִין אֶחָד, אֵי אֶפְשָׁר לְהִתְקַיֵּם. מֶה עָשָׂה? נָטַע אֶתְרוֹג בֵּינֵיהֶם, וְהוּא אֶחָד מֵאוֹתָם הַתִּשְׁעָה שֶׁעָלָה בְּלִבּוֹ לִהְיוֹת זְכָרִים. וְאֶתְרוֹג מַה נִּהְיָה? נְקֵבָה, וְהַיְנוּ שֶׁכָּתוּב (ויקרא כג) פְּרִי עֵץ הָדָר כַּפֹּת תְּמָרִים.

Yoel Domb