A friend of mine (Hi, Yoel!) pointed out a possible discrepancy in Rashi's comments on the Talmud.
On Beitzah 15b, Rashi opines (sv ופירותיה משתמרין) that אדר is a grass (עשב), against the more common opinion among the Rishonim (cited in Rashi, ibid., sv יטע בהן אדר) that the אדר is a tree.
However, Rashi to Gittin 69b (sv אטרף אדרא) refers to אדר as a tree (עץ).
Even though most Rishonim hold that אדר is a tree, Rashi in Beitzah makes it very clear that his opinion ("לי נראה") is that אדר is a grass. So why would Rashi refer to אדר as an "עץ" in Gittin?
It's worth noting that Jastrow translates אדר as "a cedar species, prob. Spanish Juniper," based (at least partially) on the discussion on Rosh Hashanah 23a, where it is said that
ד' מיני ארזים הן ארז קתרום [...] קתרום אמר רב אדרא
There are four types of cedar (ארז): erez, katrom [...] Katrom: Rav says [this is the] אדרא.
(translation mine)
Note that this gemara might change the way to ask this question -- instead of Rashi not being consistent in his translation (= "asking the kasha on Rashi Gittin"), perhaps the question needs to be asked the other way around (= "asking the kasha on Rashi Beitzah"), as Rashi didn't make a practice of disagreeing with explicit passages of Talmud. I asked the question this way because this is how my friend presented it to me.
Given the above, what should Rashi hold about the class of the אדר plant? Is it a tree (עץ), or a grass (עשב)?