Reference for Oktzin 3:7

הַקּוֹר, הֲרֵי הוּא כְעֵץ לְכָל דָּבָר, אֶלָּא שֶׁהוּא נִלְקָח בְּכֶסֶף מַעֲשֵׂר. כַּפְנִיּוֹת, אֳכָלִין, וּפְטוּרוֹת מִן הַמַּעַשְׂרוֹת:

A heart of a palm is treated like wood for all matters, except that it can be purchased with [second] tithe money. Date-berries [i.e. unripened dates] are considered food, but are exempt from tithes.

Jastrow