Lagerstroemia × egolfii Whittem. & Schori, 2022

Whittemore, Alan T. & Schori, Melanie, 2022, A new nothospecies in Lagerstroemia (Lythraceae), Phytotaxa 539 (3), pp. 294-300 : 294-299

Lagerstroemia × egolfii Whittem. & Schori , nothospec. nov.

Type:— USA. District of Columbia: North of Conifer Road just west of the old gate, Gotelli Dwarf and Low-Growing Conifer Collection, United States National Arboretum; cultivated tree, accession numbers NA 54979-CH, PI 499825, 10 September 2018, Whittemore 18-027 (holotype NA!, isotypes A!, K!, MOR!, TUS!). Figures 1–14 .

Diagnosis:— Lagerstroemia × egolfii displays a range of characters that tend to overlap with one or both parents. Leaves are smaller than those of L. fauriei , petals are as large as those of L. indica , and the hypanthium can have 12 weak veins, in contrast to the 12 strong veins of L. fauriei and the 6 veins often seen in L. indica . The full range of intermediate character states is given in Table 1 .

Large shrubs or small multitrunked trees to 7 m; main limbs spreading or upright; bark smooth, shed in thin woody strips, white to bright orange-brown where recently exposed, weathering to light or dark gray or brown. Twigs terete or 4-angled, weakly ridged. Petioles 1–3 mm long; leaf blades obovate or elliptical, 37–75 mm long, (17–) 23–43 mm wide, with (4–)5–8 secondary veins on each side of the midrib; apex rounded, obtuse, or rather short-acuminate. Inflorescences pyramidal, ultimate twigs 4-sided, ± 4-winged, puberulent, sparsely bristly, or glabrous. Hypanthium scarcely veined, or weakly 12-veined, (2–) 3–5 mm long, sepals triangular, 2–4 mm long, acute or acuminate; petals white, pink, red, or purple, claw 5–12 mm long, blade excluding claw 5–11 mm long, 7–10(–14) mm wide. Capsules spherical, 8–12 mm long; seeds with a single wing on one side.

The hybrid is named in honor of Donald Roy Egolf (1928–1990), geneticist and prolific plant breeder. Egolf led the program to utilize this hybrid horticulturally and released thirty mildew-resistant cultivars of Lagerstroemia , most of them L. × egolfii . The type was collected from a tree that is an artificial F1 hybrid between L. fauriei and L. indica ( Wang et al. 2011) . Clonal material of this plant is sometimes sold in nurseries under the cultivar name ‘Apalachee’ crape-myrtle ( Egolf 1987).

Material of Lagerstroemia × egolfii in cultivation includes F1, F2, backcross, and various later-generation hybrids. However, since horticulturists value the much larger, often colored petals of L. indica , backcrosses have been made to L. indica but seldom, if ever, to L. fauriei . This range of different genotypes recombines the characteristics of the two parents in many combinations ( Table 1 ). The description above is based on an array of F1 and later-generation hybrids.

Lagerstroemia fauriei is usually treated as a distinct species ( Koehne 1907, Ohwi 1965, Egolf & Andrick 1978, Xu et al. 2017, National Gardening Association 2018). However, some recent authors have treated L. fauriei as a variety of L. subcostata Koehne (1883: 20) , following Yahara et al. (1987). Yahara et al. published the new combination (1987: 98) but gave no justification for the change in status. They said, “This variety is distinguished from var. subcostata by its larger capsules,” but examination of living plants in the United States, plus herbarium specimens at NA and US, confirm Koehne’s contention that the two differ in characters of the bark, petiole, leaf blade, and seed, as well as the size of the capsule ( Table 2 ). In addition, Xu et al. (2017) compared complete chloroplast genomes from one accession of each taxon and found that they differed at many positions, a level of divergence more suggestive of distinct species. For these reasons, L. fauriei is treated here as a separate species.

The name Lagerstroemia × egolfii will not apply to all of the mildew-resistant hybrid crape-myrtles, since some are hybrids involving L. limii Merrill (1925: 165) , L. speciosa (Linnaeus in Münchhausen 1770: 357) Persoon (1806: 72), or L. subcostata as well as L. indica and often L. fauriei ( Wang et al. 2011) . If a name of general horticultural utility encompassing all of these plants is desired, it would be best to establish a cultivar Group under the International Code of Nomenclature for Cultivated Plants ( Brickell et al. 2016).

Figures

FIGURES 1–4. Lagerstroemia × egolfii, morphology of NA 54979-CH (‘Apalachee’), from which the type specimen was collected. 1. Habit. 2. Bark. 3. Inflorescence. 4. Flower.

FIGURES 5–13. Lagerstroemia × egolfii, variation among genotypes. 5. Habit of NA 58471 (‘Natchez’). 6. Habit of NA 54972 (‘Tonto’). 7. Bark of NA 48471 (‘Tuskegee’). 8. Bark of NA 54973 (‘Wichita’). 9. Flower of NA 38449 (‘Natchez’). 10. Flower of NA 54972 (‘Tonto’). 11–13. Capsules of NA 58471 (‘Natchez’).

FIGURE 14. Lagerstroemia × egolfii, Holotype.