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FOC | Family List | FOC Vol. 13 | Lythraceae

3. Lagerstroemia Linnaeus, Syst. Nat., ed. 10. 2: 1068, 1076, 1372. 1759.

紫薇属 zi wei shu

Authors: Haining Qin & Shirley A. Graham

Trees or shrubs. Young stems terete to frequently 4-angled or subalate, glabrous, puberulous, pubescent, or tomentose, often glabrescent. Leaves variably subopposite to subalternate or alternate, rarely opposite or truly alternate, subsessile or petiolate; stipules minute, caducous. Inflorescences terminal and axillary paniculate cymes. Flowers actinomorphic, campanulate to turbinate, flexibly 5-7-merous. Floral tube leathery, smooth walled with 6-12(-14) veins visible as dark lines, or with broad to narrow ribs or ridges; sepals narrowly to broadly deltate, sometimes subtended within by a narrow annulus; epicalyx segments alternating with sepals, small to prominent, or absent. Petals 6(-12), rose, purple, or white, crinkled, slenderly clawed. Stamens (6-)12-100+, inserted at or near base of floral tube, exserted, dimorphic in most species, 6 solitary in front of sepals with thick filaments and large anthers, 12-100+ in clusters in front of petals with thin filaments and small anthers, rarely monomorphic, then all filaments thin, subequal. Ovary globose to oblong, 3-6-loculed; style long-exserted; stigma capitate. Fruit dry, indurate capsules, surrounded at base by persistent floral tube, loculicidally dehiscent, 3-6-valved. Seeds numerous, obpyramidal, unilaterally winged from raphe; cotyledons rolled.

About 55 species: tropical and subtropical Asia to Australia, north to Japan; 15 species (eight endemic) in China.

Lagerstroemia is in need of more extensive gatherings and study in order better to understand the extent of variability among and within the species.

The flowers are typically 6-merous, but can be 5-7-merous on the same plant. The floral tubes contract ± abruptly below the base of the ovary (campanulate) or taper gradually to the paired bracteoles of the pedicel (turbinate). The length of the floral tube is measured from the base of the ovary to the apex of the sepals; the pedicellate base (epipodium) extending from the base of the ovary to the bracteoles is not included.

A specimen of Lagerstroemia micrantha Merrill (J. Arnold Arbor. 21: 378. 1940, described from Vietnam) was reported by Furtado and Montien (Gard. Bull. Singapore 24: 276. 1969) from Taiwan (Faurie 8076, A) but without further information. One of us (Graham) saw this specimen, and another so named, at US from Hong Kong, but without collector or further data. Inclusion of L. micrantha in this Flora is deferred until the taxonomic status of the species is better understood.

In addition to the species mentioned below as being cultivated in China, the following have also been recorded as cultivated: Lagerstroemia siamica Gagnepain (native to Malaysia, Myanmar, and Thailand) in Taiwan (1950, no further data, A); L. reginae Roxburgh (native to India, Myanmar, and New Guinea) in Guangzhou (Hooker s.n., E); and L. floribunda var. brevifolia Craib (native to Cambodia and Thailand) without locality (Macartney s.n., BM).

1 Leaves, panicles, and flowers densely tomentose; trichomes dendritic, golden- to red-brown   (2)
+ Leaves, panicles, and floral tubes glabrous, variously pubescent, or puberulous (grayish tomentose in L. suprareticulata); trichomes simple, grayish white or yellow-brown   (3)
2 (1) Ovary and adaxial surface of sepals densely tomentose; floral tube smooth walled, densely tomentose, 10-12 mm.   1 L. balansae
+ Ovary densely tomentose, adaxial surface of sepals completely glabrous; floral tube 12-ribbed, 8-10 mm.   2 L. tomentosa
3 (1) Floral tubes prominently undulate-winged from sinus of sepals, wings attenuate on pedicellate floral base; floral tubes densely white pubescent; epicalyx absent.   3 L. villosa
+ Floral tubes smooth walled or 6-12(-14)-ribbed; ribs broad and flat or sharply ridged, without undulate wings; floral tubes glabrous or pubescent; epicalyx present or absent   (4)
4 (3) Epicalyx prominent at sinus between sepals   (5)
+ Epicalyx absent or minute at sinus between sepals   (7)
5 (4) Epicalyx segments broad, flat, auriculate, ca. 1/2 as long as sepals; sepals deltate with caudate apex   4 L. limii
+ Epicalyx segments linear or deltate and keeled, ca. as long as sepals; sepals deltate with acute to shortly acuminate apex   (6)
6 (5) Epicalyx segments linear, ca. as long as or surpassing sepals; branchlets and panicles glabrous; floral tubes prominently sharply 6-ribbed.   5 L. guilinensis
+ Epicalyx segments deltate, abaxially keeled, slightly incurved in bud; branchlets and panicles densely gray puberulous; floral tubes 6- or 7-ribbed; ribs rounded or obscure.   6 L. venusta
7 (4) Floral tubes 7-15 mm from apex of sepals to base of ovary   (8)
+ Floral tubes 2-5 mm from apex of sepals to base of ovary   (11)
8 (7) Floral tubes glabrous, smooth walled or obscurely to decidedly 6-ribbed; leaves, at least some, suborbicular to obovate, 2.5-7(-10) × 1.5-4 cm.   7 L. indica
+ Floral tubes gray or yellow-brown puberulous or pubescent, obscurely to distinctly 12-ribbed or dark veined; leaves ovate-elliptic or lanceolate   (9)
9 (8) Floral tubes yellow-brown puberulous, (8-)12-15 mm; sepals adaxially glabrous; leaves 7-18 × 4-8 cm, apex shortly acuminate; stamens 70 to ca. 130.   8 L. intermedia
+ Floral tubes gray pubescent or tomentose, 9-11 mm; sepals adaxially sparsely to densely gray-pubescent or tomentose; leaves 3-10 × 2.5-4 cm, apex shortly to long acuminate or caudate; stamens 25-40   (10)
10 (9) Floral tubes distinctly 10-12-ribbed; leaves (3-)6-10 × 2.5-4 cm, adaxial venation not raised, apex acuminate to caudate; sepals adaxially sparsely pubescent in distal half   9 L. fordii
+ Floral tubes ± smooth walled with (10-)12 dark veins; leaves 4-6.2 × 2.5-3.5 cm, adaxial venation distinctly raised, apex shortly acuminate; sepals adaxially densely gray tomentose.   10 L. suprareticulata
11 (7) Branchlets yellow-brown pubescent; floral tubes distinctly 8-12-ribbed; sepals adaxially densely pubescent.   11 L. anhuiensis
+ Branchlets glabrous or gray puberulous to pubescent; floral tubes smooth walled with 10-12(-14) dark veins or obscurely 12-ribbed; sepals adaxially glabrous or sparsely puberulous   (12)
12 (11) Stamens 6-12; sepals adaxially sparsely puberulous at apex.   12 L. excelsa
+ Stamens 15-30, mostly more than 20; sepals adaxially glabrous   (13)
13 (12) Petals broadly ovate, claw ca. as long as blade, 7-10 mm including claw 3.5-6 mm, white, pink, or purple, base rounded to obtuse; leaves ovate to lanceolate, or elliptic, or less often obovate, 2-9(-11) × 1-5 cm.   13 L. subcostata
+ Petals lanceolate, oblong, or elliptic, claw shorter than blade, 6-9 mm including claw 1.5-3 mm, white, base acute; leaves broadly elliptic or ovate to elliptic or lanceolate, 4.5-12 × 2.2-5 cm   (14)
14 (13) Leaves ovate-elliptic or ovate-lanceolate, 4.5-6.5(-11) × 2-3(-4) cm; petiole 2-5 mm; ultimate branches of inflorescence glabrous; petals 6-7 mm; capsules 6-8 × 4-5 mm.   14 L. glabra
+ Leaves broadly elliptic, 7-12 × 3-5.5 cm; petiole 6-10 mm; ultimate branches of inflorescence puberulous; petals ca. 9 mm; capsules 8-11 × 6-9 mm.   15 L. caudata

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