Neotropical Lythraceae

Shirley Graham* & Taciana Barbosa Cavalcanti** 

Missouri Botanical Garden, St. Louis, USA.*
Embrapa Recursos Genéticos e Biotecnologia - Embrapa Cenargen, Brasília, Brazil.**   

Description

Trees, shrubs or herbs, younger stems often quadrangulate.  Leaves opposite, less often whorled or subalternate, simple, entire, estipulate, colleters present in leaf axils; blades membranous or coriaceous, venation brochidodromousInflorescences indeterminate, racemes, cymes, or clusters, rarely flowers solitary; pedicels with prophylls (bracteoles).  Flowers actinomorphic or zygomorphic, perfect, perigynous, (4)- 4-6 -(16)-merous; floral tube campanulate to tubular, often conspicuously veined, persistent except in Lafoensia; sepals valvate, petals (0)-4-6(-many), inserted on the inner rim of floral tube, alternating with sepals, crinkled, pinnately veined, caducous; stamens diplostemonous, sometimes reduced to a single whorl; gynoecium syncarpous, nectariferous tissue present or absent; style simple, slender, commonly exserted, stigma capitate or punctiform; ovary superior, infrequently semi-inferior, (2)-2-4(-many) locular, septa incomplete at apex or vestigial, reduced to thin threads, placentation axile, or globose and nearly free -central.  Fruits dry, thin or thick-walled capsules enclosed by persistent floral tube, dehiscing loculicidally, septicidally, or splitting irregularly.  Seeds numerous, obpyramidal, or oblong to obovoid and concave-convex, or bilaterally lenticular-compressed, winged or not, with inverted epidermal trichomes in seed coat; embro straight, cotyledons planar, auriculate or cordate, oily.  x = 8.

Notes on delimitation

  • Based on molecular evidence, the Combretaceae is sister to the Lythraceae and the Onagraceae. The three families constitute a major lineage of the Myrtales. 
  • Recent molecular work has led to the expansion of the family to include the satellite families Sonneratiaceae, Duabangaceae, Punicaceae and Trapaceae.

Distribution in the Neotropics

  • Adenaria Kunth (1/1 sp.) - limited to South America and Central America.
  • Ammannia L. (4/25 spp.) - Old world and New World distribution.
  • Crenea Aubl. (2/2 spp.) - New World only.
  • Cuphea P. Browne (c. 240/c. 240 spp.) - limited to South America, Central America, Mexico, Caribbean, and United States.
  • Diplusodon Pohl (85/85 spp.) - New World only.
  • Ginoria Jacq. (13/13 spp.) - present in Greater Antilles and Mexico.
  • Heimia Link (3/3 spp.) - limited to South America, Central America, Mexico, Caribbean, and United States.
  • Lafoensia Vand. (c. 5/c. 5 sp.) - limited to South America and Central America.
  • Lourtella Graham, Baas, & Tobe (1/1 sp.) - New World only.
  • Lythrum L. (2/35 spp.) - Old world and New World distribution.
  • Nesaea Comm. (3/c. 50 spp.) - Old world and New World distribution.
  • Pehria Sprague (1/1 sp.) - limited to South America and Central America.
  • Physocalymma Pohl (1/1 sp.) - New World only.
  • Pleurophora D. Don (c. 6/c. 6 spp.) - New World only.
  • Rotala L. (2/44 spp.) - Old world and New World distribution.

Distinguishing characters (always present)

  • No unique synapomorphies.

Other important characters

  • Opposite entire leaves.
  • Flowers 4-6-merous, but 8-merous in Physocalymma, up to 16-merous in Lafoensia, perigynous, ovary superior, infrequently semi-inferior.
  • Crinkled petals, often fugacious.
  • Stamens 2-whorled (obdiplostemonous), deeply inserted.
  • Seeds in most New World genera with inverted trichomes in the epidermal cells of the seed coat that evert on wetting: trichomes spiraled in Cuphea, Lafoensia, Pehria, Pleurophora; trichomes straight in Ammannia, Crenea, Diplusodon, Ginoria, Heimia, Lythrum, Nesaea, Rotala.

Key differences from similar families

Number of genera

  • 15 native genera: Adenaria, Ammannia, Crenea, Cuphea, Diplusodon, Ginoria (including Haitia), Heimia, Lafoensia, Lourtella, Lythrum, Nesaea, Pehria, Physocalymma, Pleurophora, Rotala.

Useful tips for generic identification

Key to genera of Neotropical Lythraceae

1. Leaves glandular-punctate, the punctae non-secretory and orange-filled, turning black or secretory and translucent.
1. Leaves non-punctate, glabrous or variously indumented ... 4

2.  Leaves orange to black-punctate, non-secretory; inflorescences multi-flowered clusters ... 3
2.  Leaves translucent-punctate, secretory, blades varnished by resin; inflorescences 3-flowered axillary cymes ...Lourtella

3.  Flowers in compact umbelliform clusters; floral tube campanulate, greenish; capsule indehiscent...Adenaria
3.  Flowers in loose cymose clusters; floral tube cyathiform, deep red; capsule loculicidally dehiscent...Pehria

4.  Floral tubes campanulate to globose or cyathiform, about as long as to slightly longer than wide, actinomorphic... 5
4.  Floral tubes cylindrical, at least twice as long as wide, actinomorphic or zygomorphic... 13

5.  Seeds encircled by a broad, thin wing … 6
5.  Seeds not winged... 8

6.  Floral tubes caducous, distally pleated, (8-)10-12(-16)-merous; leaves with subapical abaxial porate chamber ...Lafoensia
6.  Floral tubes persistent, distally smooth, 6- or 8-merous; leaves normally developed at the apex, lacking a porate chamber ... 7

7.  Trees with strongly divaricate branching; flowers 8-merous; placenta appearing free -central ...Physocalymma
7.  Shrubs and subshrubs with opposite branching; flowers 6-merous; placenta bipartite, septa lunate ...Diplusodon

8.  Trees, shrubs, or subshrubs, 1-40 m ... 9
8.  Annual or perennial herbs, 2 cm - 2m, commonly less than 50 cm ... 1

9.  Stamens basifixed; petals cream-coloured; capsules indehiscent... Crenea
9.  Stamens dorsifixed; petals bright yellow, rose, purple, or white ... 10

10.  Petals bright yellow; flowers solitary; pedicels 0-4 mm ...Heimia
10.  Petals rose, purple, or white; flowers solitary and/or in axillary clusters; pedicels 10-40 mm ...Ginoria

11.  Capsules septicidally dehiscent, wall microscopically (10x) transversely striated; leaves decussate or whorled; leaf base tapered ...Rotala
11.  Capsules splitting irregularly or initially circumscissile, then irregular; wall microscopically smooth, without striations; leaf base auriculate or auriculate... 12

12.  Capsules splitting irregularly; leaf base auriculate...Ammannia
12.  Capsules initially circumscissile, then splitting irregularly; leaf base cordate...Nesaea

13.  Floral tubes actinomorphic;capsules dehiscing from the apex...Lythrum
13.  Floral tubes slightly to strongly zygomorphic, bilateral; capsules indehiscent or dehiscent dorsally by a longitudinal slit together with floral tube ... 14

14.  Stamens attached near base of floral tube, anthers basifixed; capsules indehiscent, placenta and seeds retained within ... Pleurophora
14.  Stamens attached at midlevel or higher in floral tube, anthers dorsifixed; capsules dehiscent dorsally by a longitudinal slit together with floral tube, placenta and seeds exserted...Cuphea

Notable genera and distinguishing features

  • Cuphea - largest genus of the family, c. 240 spp.  Endemic to New World.  Unique capsule dehiscence by a longitudinal slit with placenta and seeds emerging for seed dispersal.  Seed oils emphasize lauric acids and diversity of composition includes some with major percentages of caprylic acid.
  • Diplusodon - second largest genus of the family, c. 85 spp. Endemic to Brazil and adjacent Bolivia.
  • Heimia -  hallucenogenic, anti-inflammatory.

Status

  • Three non-native genera cultivated in the Neotropics: Lagerstroemia (crape myrtle), Lawsonia (henna), Punica (pomegranate).

General notes

  • Waiting publication: Haitia synonymized with Ginoria in Graham, S. A. (2009, in press).  Revision of the Caribbean Genus Ginoria (Lythraceae), including Haitia from Hispaniola.  Ann. Missouri Bot. Garden.

Important literature

Cavalcanti, T. B.  (in press). Revision of Diplusodon (Lythraceae).  Fl. Neotropica.

Graham, S. A.  1988.  Revision of Cuphea section Heterodon (Lythraceae).  Systematic Botany Monographs. 20: 1-168.

Graham, S. A.  1989.  Revision of Cuphea sect. Leptocalyx (Lythraceae).  Systematic Botany monographs 14: 43-76.

Graham, S. A. 1998.   Revision of Cuphea sect. Diploptychia (Lythraceae). Systematic Botany monographs 53: 1-96.

Graham, S. A.  2010.  Revision of the Caribbean genus Ginoria (Lythraceae), including Haitia from Hispaniola.  Annals of the Missouri Botanical Garden 97: 34-90.

Koehne, E.  1903.  Lythraceae.  326 pp. In: Engler, A. ed., Das Pflanzenreich IV. 216.

Lourteig, A.  1986.  Revision del genero Lafoensia Vandelli (Litraceas).  Mem. soc. ci. Nat. La Salle 45: 115-157.

Lourteig, A.  1986.  Revision del genero Crenea Aublet (Litraceas).  Caldasia 15: 121-142.

Lourteig, A.  1986.  Revision de dos secciones del genera Cuphea P. Browne (Lythraceae).  Phytologia 60: 17-55.

Lourteig, A.  1988.  Revision de Cuphea P. Browne seccion Heteranthus Koehne (Litraceas).  Mutisia 70: 1-20.

How to cite

Graham, S. & Cavalcanti, T.B. (2009). Neotropical Lythraceae. In: Milliken, W., Klitgĺrd, B. & Baracat, A. (2009 onwards), Neotropikey - Interactive key and information resources for flowering plants of the Neotropics. http://www.kew.org/science/tropamerica/neotropikey/families/Lythraceae.htm.