Cenchrus polystachios subsp. polystachios, a species of Sandburs
Hello. This is called black fountain grass (Cenchrus purpurascens). https://www.marylandbiodiversity.com/viewSpecies.php?species=16133 It is a non-native ornamental grass that has spread beyond home landscapes and has become invasive in some natural areas. We do not recommend planting it. These plants can be very difficult to remove when they end up in places where you do not want them.
Here is our information about invasive plants.
I encourage you to consider some of our native grasses. Little bluestem and yellow Indiangrass are a couple of nice choices. https://extension.umd.edu/hgic/topics/recommended-native-plants-maryland