וַיֹּ֣אמֶר אֱלֹהִ֗ים תַּֽדְשֵׁ֤א הָאָ֙רֶץ֙ דֶּ֔שֶׁא עֵ֚שֶׂב מַזְרִ֣יעַ זֶ֔רַע עֵ֣ץ פְּרִ֞י עֹ֤שֶׂה פְּרִי֙ לְמִינ֔וֹ אֲשֶׁ֥ר זַרְעוֹ־ב֖וֹ עַל־הָאָ֑רֶץ וַֽיְהִי־כֵֽן׃
Und Gott sprach: Es lasse die Erde Grünes hervorsprießen, Kraut, das Samen bringt, Fruchtbäume, die Frucht tragen, jeder nach seiner Art, in denen ihr Same ist, auf der Erde; und es ward also.
Rashi on Genesis
תדשא הארץ דשא עשב THE EARTH SHALL SPROUT FORTH SPROUTS, HERB — דשא does not mean the same as עשב nor does עשב mean the same as דשא so that it is not a correct expression in Biblical Hebrew to say תעשיב הארץ, for the species of דשא are all different, each by itself being called this or that עשב, and it would not be linguistically correct for a speaker to say this or that דשא, for by דשא is meant that which forms the covering of the ground when it is filled with herbage.
Rashbam on Genesis
דשא, every kind of herb collectively is known as דשא whereas every individual type of herb is known as עשב.
Sforno on Genesis
דשא, herbs fit for consumption by animals. We find this expression used in this sense in Yoel 2,22כי דשאו נאות מדבר, “for its herbs (the ones for the beasts) are found in the pastures of the wilderness.”