"莓系属的牧草" can be translated as "forage grasses of the Rubus genus (or relevant genera if '莓系属' refers to a broader group related to berries; note that '莓系属' is not a standard botanical classification in English, so the exact translation may vary based on context)" .
However, if we're strictly interpreting "莓系属" as a genus-like group related to berries (though not a standard scientific term), and assuming it refers to plants similar to those in the Rubus genus (like raspberries, blackberries, etc.), but applied to forage grasses (which is a bit unusual as grasses and berries belong to different plant families), a more context-appropriate translation might need to be adjusted.
A more common and accurate way to express the idea, if referring to forage grasses that are somehow related to or beneficial for environments where berry-producing plants grow, might be phrased differently, such as "forage grasses suitable for berry-producing environments" or "forage grasses compatible with berry cultivation."
But directly translating "莓系属的牧草" as literally as possible while acknowledging the non-standard botanical term, the above initial translation is provided. In a scientific or specific agricultural context, further clarification of "莓系属" would be needed for a more precise translation.