Does an orange belong on the seder plate?

A popular Jewish feminist practice is apparently to place an orange on the seder plate. The popular basis of it, which I also heard in shiur once, is as follows:

It all began when Susannah Heschel, a leading Jewish feminist scholar, was lecturing at a synagogue in Miami. As she spoke, an elderly rabbi stood up and declared, "A woman belongs on the bimah like an orange belongs on the seder plate."

Thus to show support for the changing role of women in American Jewish society, the tradition of placing an orange on the seder plate began, and Heschel became a household name at many Passover celebrations around the globe.

According to the above-linked article, though, this isn't true. Rather, students were putting chametz on the seder plate in solidarity with women and homosexuals, excluded from Judaism; Heschel saw this, and replaced it with an orange in subsequent years. (h.t. for linking to the article: DovBear)

But does an orange have a place on the seder plate? It already does, as one of the components of the charoses! The gemara in Pesachim 116a:

רבי אלעזר בר' צדוק אומר מצוה וכו':

מאי מצוה רבי לוי אומר זכר לתפוח ור' יוחנן אומר זכר לטיט 

אמר אביי הלכך צריך לקהוייה וצריך לסמוכיה 

לקהוייה זכר לתפוח וצריך לסמוכיה זכר לטיט 

תניא כוותיה דרבי יוחנן תבלין זכר לתבן חרוסת זכר לטיט אמר רבי אלעזר בר' צדוק כך היו אומרים תגרי חרך שבירושלים בואו וטלו לכם תבלין למצוה:

One needs to make the charoset sour (ascerbic), as a zecher to the tapuach. What tapuach?

Rashi writes:

זכר לתפוח - שהיו יולדות בניהן שם בלא עצב שלא יכירו בהן מצריים דכתיב תחת התפוח עוררתיך (שיר ח'):

That they gave birth without pain. That pasuk is:

ה  מִי זֹאת, עֹלָה מִן-הַמִּדְבָּר, מִתְרַפֶּקֶת, עַל-דּוֹדָהּ; תַּחַת הַתַּפּוּחַ, עוֹרַרְתִּיךָ--שָׁמָּה חִבְּלַתְךָ אִמֶּךָ, שָׁמָּה חִבְּלָה יְלָדַתְךָ.

5 Who is this that cometh up from the wilderness, leaning upon her beloved? Under the apple-tree I awakened thee; there thy mother was in travail with thee; there was she in travail and brought thee forth.

Except, according the Rav Soloveitvchik, the tapuach mentioned in this gemara is a citrus fruit, which is sour. And therefore, as discussed in this previous parshablog post, Rav Schachter therefore puts citrus fruit into his charoses. In that case, there should be orange on the seder plate.

I see that Feliks discusses the identity of the tapuach in Tanach and Chazal, in his book צי־פרי למיניהם, צמחי התנ״ך וחז״ל. Does anyone have a copy of this book, who could summarize for me his conclusions and proofs as to the identity of the tapuach?