| Author | Engelmann | |
| Distribution | Throughout the eastern half of the Piedmont, and extending into the western and central Coastal Plain along large brownwater river floodplains (mainly the Roanoke and Cape Fear). Scattered in the Mountains and western half of the Piedmont, locally absent.
This is a Southern species ranging north only to southern PA and MO, and south to northern FL and central TX. It is scarce in the Appalachian Mountains.
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| Abundance | Fairly common to locally common in the eastern half of the Piedmont. Locally fairly common along the Roanoke and Cape Fear rivers well into the Coastal Plain. Rare to uncommon in the central Mountains, but very rare in the western Piedmont and much of the Mountains. It arguably could be given a State Rank of S5, instead of the NCNHP's S4 rank. | |
| Habitat | This is a semi-wetland species that requires rich, usually alluvial, soil. It grows best on natural levees, as well as in rich bottomland forests. However, it does well in partial shade and in disturbed ground, as long as it is rich and moist. Thus, it occurs in bottomland openings, floodplain clearings, and other similar sites. It can, at times, be found on lower rich forested slopes, such as in Basic Mesic Forests. | |
| Phenology | Blooms in April and May, and fruits shortly after flowering. It withers to the ground by the end of May. | |
| Identification | This species and M. verna are quite similar species, with similar ranges in the state, though this one is a species of rich and moist ground, usually in shaded conditions, and is a more robust species than is the smaller M. verna. This species reaches about 1.5 feet tall, rarely 2 feet tall, with a few branches. The stem leaves are alternate, oblong to oblanceolate, and about 2 inches long, mostly sessile. The slender racemes of small white flowers are at the ends of the branches; they eventually grow to be long and lanky. Each flower is barely 1/10-1/8-inch wide, with 5 lobes. The main separation from M. verna is that M. macrosperma has the flowers more spread apart from each other on the raceme axis, typically more than 1 cm (2/5-inch) from neighboring flowers, and the lower ones often 2 cm apart (4/5-inch); M. verna has the flowers closer to each other, less than 2/5-inch apart. That species has the stalks when in fruit more or less erect, whereas M. macrosperma has the pedicels in fruit divergent from the raceme axis. As a general rule, if the plant is growing in rich soil and usually in a floodplain, and it does not look hairy, it should be this species, as opposed to a smaller and more pubescent one growing in dry soil in upland openings. | |
| Taxonomic Comments | None
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| Other Common Name(s) | Bigseed Forget-me-not | |
| State Rank | S4 [S5] | |
| Global Rank | G5 | |
| State Status | | |
| US Status | | |
| USACE-agcp | FAC link |
| USACE-emp | FAC link |
