Magnolia macrophylla has three subspecies; some botanists treat these plants as three separate species:
Magnolia macrophylla subsp. macrophylla. Bigleaf magnolia. Southeastern United States. Secure. Tree to 20 m; leaves 50–90 cm long, fruit 4–10 cm long with more than 50 carpels.
Magnolia macrophylla subsp. ashei Spongberg. Ashe magnolia. Northwest Florida. Shrub or small tree to 12 m; leaves 25–60 cm long, fruit 4–5 cm long with less than 50 carpels. Considered by some botanists to be a distinct species, Magnolia ashei.
Magnolia macrophylla subsp. dealbata J. D. Tobe. Mexican bigleaf magnolia or Cloudforest magnolia. Mexico. Tree to 20 m; leaves 30–60 cm long, fruit 8–15 cm long with more than 70 carpels. Considered by some botanists to be a distinct species, Magnolia dealbata.
Description
Bigleaf magnolia is medium-sized understory tree 15–20 m tall, though some individuals over 27m tall have been documented by the . This species is distinguished from other magnolias by the large leaf size, 25–80 cm long and 11–30 cm broad. The tree's branches often bend under the weight of this heavy foliage.
Distribution and habitat
Bigleaf magnolia is found in rich mesic woods; any disturbance that lets more light reach the ground is beneficial to the establishment of bigleaf magnolia, but despite its relatively fast growth-rate when stimulated by more light, other understory and canopy trees/seedlings are usually able to outgrow and out-compete it. This suits the plant just fine as it is tolerant of low light levels; it does not need full sun to survive once established. Natural regeneration is quite limited due to the scarcity of mature, seed-bearing plants and the fact that this tree's population mostly consists of widely scattered individuals. In addition, this species is plagued by poor seed set and low seed :wikt:viable|viability, a trait shared by its cousin and frequent associate in the wild in Appalachia, the Fraser magnolia. The Ashe magnolia is a rare shrub, exceptionally a small tree, that is found only along the bluffs and ravines adjacent to the Apalachicola River in Florida, along with several other rare plants unique to the area, such as Florida Yew and Florida torreya. It resembles the typical subsp. macrophylla, but has shorter, broader leaves, smaller flowers, and longer fruits. The flowers bloom in late spring, and are white with rose-purple blotches on the inner tepals. The fruit is eaten by wildlife, but because of the plant's scarceness, it does not form a significant portion of any creature's diet. In the southeastern United States, especially Alabama and surrounding areas, Magnolia macrophylla is sometimes called the "cowcumber magnolia," in contrast with the much smaller-leaved cucumber-tree magnolia, M. acuminata.
Bigleaf magnolia is often short-lived under cultivation unless its rather demanding requirements are met. This tree likes loose, undisturbed rich mesic soil in full sun or part shade with moist, well-drained soil and a low pH. This tree will likely succeed in sites that closely mimic its natural habitat and where it is protected from strong wind that can tatter its large foliage. It can be grown farther north than its southerly range suggests, but needs watering during extended dry periods. This plant is generally problem free.
