א עַרְבֵי נַחַל הָאָמוּר בַּתּוֹרָה, הוּא מִין יָדוּעַ הַנִּקְרָא כֵּן; עָלֶה שֶׁלּוֹ מָשׁוּךְ כְּנַחַל, וּפִיו חָלָק, וְקָנֶה שֶׁלּוֹ אָדֹם וַאֲפִלּוּ בְּעוֹדוֹ יָרֹק, כָּשֵׁר (בֵּית יוֹסֵף); וְרֹב מִין זֶה גָּדֵל עַל הַנְּחָלִים, לְכָךְ נִקְרְאוּ עַרְבֵי נַחַל, וַאֲפִלּוּ הָיָה גָּדֵל בַּמִּדְבָּר אוֹ בֶּהָרִים, כָּשֵׁר; וְיֵשׁ מִין אֶחָד דּוֹמֶה לָעֲרָבָה, אֶלָּא שֶׁעָלֶה שֶׁלּוֹ עָגֹל וּפִיו דּוֹמֶה לְמֶסֶר (פֵּרוּשׁ מָגֵרָה סיג"ה בְּלַעַ"ז) וְקָנֶה שֶׁלּוֹ אֵינוֹ אָדֹם, וְזֶהוּ הַנִּקְרָא: צַפְצָפָה, וְהִיא פְּסוּלָה; וְיֵשׁ מִין עֲרָבָה שֶׁאֵין פִּי הֶעָלֶה שֶׁלָּהּ חָלָק וְאֵינוֹ כְּמֶסֶר, אֶלָּא יֵשׁ בּוֹ תְּלָמִים קְטַנִּים עַד מְאֹד כְּמוֹ פִּי מַגָּל קָטָן, וְזֶה כָּשֵׁר.
1 The Laws of the Aravah (Willow), 2 Seifim: "Willows of the stream" mentioned in the Torah is a known species that is called that. Its leaf is long like a stream, its leaf edge is smooth, and its stem is red (and even when it is still green it is valid (Beit Yosef)). Most of this species grows by streams, which is why it is called "willows of the stream." Even if it were to grow in the desert or the mountains, it is valid. There is another species similar to the willow but with round leaves with edges serrated like a massar (meaning a sickle, siga in the vernacular) and a non-red stem. This is the tzaftzfa, and it is invalid. There is a kind of willow whose leaf edge is not smooth but rather has many small protrusions like a small sickle, and it is valid.