Neotropical Loasaceae

Max Weigend

Institut für Biologie - Systematische Botanik und Pflanzengeographie, Berlin, Germany. 


Usually annual, biennial or perennial herbs, sometimes winding, rarely subshrubs, very rarely woody lianas or cushion-forming plants, thickend storage roots sometimes present. Leaves usually opposite below and alternate above, rarely opposite or alternate throughout, simple or compound, mostly widely ovate with lobed margin, lobes lobulate and serrate, sometimes pinnate or bipinnate or palmatifid, very rarely cordate with acuminate tip and entire margin or linear, or lyrate with undulate or pinnatifid/-sect margin; estipulate but pseudostipules rarely present. Inflorescences terminal, thyrsoids, rarely monochasial or dichasial cymoids, sometimes apparently single and axillary, very rarely in racemes or in heads; inflorescence bracteose or frondose, very rarely ebracteose. Flowers hermaphrodite, (4-)5(-8)-merous, actinomorphic or very weakly zygomorphic; sepals well developed, sometimes larger than petal, entire or dentate, sometimes pinnate; petals often white, or yellow, orange, pink, red, sometimes two-coloured; stamens 5-10-40-100-150, antesepalous, obdiplostemonous, or polyandrous, then often outer ones with dilated filaments or petaloid, or fertile antepetalous fascicles with stamens reflexed into petals alternating with antesepalous staminodial groups, these often (subfam. Loasoideae) modified into staminodial complexes (typically 3 outer ones fused into floral scale, 2 inner ones free but closing the adaxial side of the scale), floral scale extremely variable in size, shape, ornamentation and colouration, ofter 2-3-coloured; ovary syncarpous, hypogynous, of 3--5 carpels, unilocular, single style with very long but nearly or completely coherent stigmatic lobes. Nectary disc absent or present and cup-shaped, or nectaries in 5 antesepalous bulges. Fruit crowned with persistent, sometimes accrescent calyx, sometimes single-seeded and indehiscent, usually a many-seeded capsule opening with 3-5 apical valves, or with 3-10 longitudinal slits, seeds 1-3,000, rarely smooth, usually with at least reticulate testa, often with complex honeycomb pattern, or lateral or terminal wings.

Notes on delimitation

  • Members of the Loasaceae represent a well-supported monophylum, in spite of their wide variability in most morphological characters.
  • Its closest ally is Hydrangeaceae, with some striking morphological similarities (flower, fruit, seed and leaf) between genera such as Deutzia Thunb., Philadelphus L. and Jamesia Torr. & A.Gray of that family and Klaprothieae of Loasaceae.

Distribution in the Neotropics

Loasaceae comprise 20 genera and over 300 species. Virtually all of them belong to the New World and ca. 200 species are found in the Neotropics. Only the genera Kissenia R.Br. ex T.Anderson (Africa, Arabia) and Plakothira J.Florence (Polynesia) are extra-American. 50 genera and 500 species occur in the Neotropics. Representation of genera:

  • Aosa Weigend (7 species) Brazil, Hispaniola.
  • Blumenbachia Schrad. (12 species) Brazil, Uruguay, Paraguay, Argentina, Chile.
  • Caiophora C.Presl (ca. 50 species) Peru, Bolivia, Argentina, Chile, Uruguay, Brazil, Ecuador.
  • Cevallia Lag. (1 species) SW USA and N Mexico.
  • Chichicaste Weigend (1 species) NW Colombia to Costa Rica.
  • Eucnide Zucc. (13 species), Guatemala, Mexico to SW USA.
  • Fuertesia Urb. (1 species) Hispaniola.
  • Gronovia L. (2 species) NW Peru to Mexico.
  • Huidobria Gay (2 species) Chile.
  • Klaprothia Kunth (2 species) S Mexico to Brazil and Bolivia, also Caribbean, Galapagos.
  • Loasa Adans. (36 species) Chile, Argentina, Peru.
  • Mentzelia L. (80 species) Argentina to Canada, Caribbean and Galapagos Is., most SW USA and Mexico.
  • Nasa Weigend (100 species) Colombia, Ecuador, Peru, Chile, Bolivia, Venezuela, C America to S Mexico.
  • Petalonyx A.Gray (5 species) N Mexico and SW USA.
  • Presliophytum ( Urb. & Gilg ) Weigend (3 species) Peru.
  • Schismocarpus S.F.Blake (1 species) Mexico.
  • Scyphanthus D.Don (1-2 species) Chile.
  • Xylopodia Weigend (1 species) Peru.

Distinguishing characters (always present)

  • Predominantly herbs with scabrid or glochidiate indumentum.
  • Stinging hairs often present.
  • Inferior ovary with 3--5 carpels and intrusive-parietal placentation.
  • Single style with very short, stigmatic lobes or without .
  • Fruits mostly capsules opening with apical valves.

Key differences from similar families

Members of the Loasaceae are sometimes confused with Cucurbitaceae or Malvaceae: 

Number of genera

  • Twenty Neotropical genera.  Subfamily Loasoideae comprises ca. 200 species and thus nearly 2/3rds of the species of the family. Ca. 190 of these are South American.

Notable genera and distinguishing features

  • Nasa: monochasia with a single bract per flower, strongly urticant.
  • Caiophora: fruits opening with longitudinal slits, strongly urticant.
  • Scyphanthus: fruits linear, not urticant.
  • Blumenbachia: all fruits twisted in the same direction (anticlockwise), all leaves opposite.
  • Eucnide: flower polyandrous and filaments basally fused with corolla, staminodia absent, plants urticant.
  • Schismocarpus: obdiplostemonous, narrowly endemic in S Mexico.
  • Petalonyx: inflorescence racemose, filaments inserted between petals or apparently outside petals.
  • Gronovia: haplostemonous, winding and urticant with deeply lobed leaves.
  • Fuertesia: haplostemonous, woody liana with cordate, entire, coriaceous leaves.
  • Klaprothia: flowers tetramerous, white, antesepalous staminodia free, yellow, common weed.
  • Xylopodia: flowers tetramerous, green, antesepalous staminodia united into green floral scale with yellow apex, very narrowly endemic in Prov. Contumazá, N Peru.


  • All species are native, and many species are very narrowly endemic.
  • Mentzelia aspera Vell. is likely to have originated in N Central America and has probably been spread as a weed.

General notes

  • The family is a potential source of highly unsaturated oils from the seeds.
  • Several species are used in traditional medicine, but only one is found in international trade and only to a very limited extent (Mentzelia scabra subsp. chilensis (Gay) Weigend).
  • Many species, especially in Aosa, Nasa, Caiophora and Loasa, have extremely painful stinging hairs.
  • A large number of species, especially of the genus Nasa, are very narrowly endemic, some only known from the type collection, and at least 2 already extinct (N. hastata (Killip) Weigend from C Peru and N. humboldtiana subsp. humboldtiana (Urb. & Gilg) Weigend from S Ecuador).

Important literature

Ackermann, M. & Weigend, M. (2006). Nectar, Floral Morphology and Pollination Syndrome in Loasaceae subfam. Loasoideae (Cornales). Annals of Botany. 98: 503-514.

Ackermann, M. & Weigend, M. (2007). Notes on the genus Caiophora C.Presl (Loasoideae, Loasaceae) in Chile and neighbouring Peru. Darwiniana 45(1): 45-67.

Ackermann M., Achatz, M. & Weigend, M. (2008). Hybridization and crossability in Caiophora (Loasaceae subfam. Loasoideae): Are interfertile species and inbred populations results of a recent radiation? Am.  J.  Botany 95: 1109-1121.

Aitzetmüller, K., L. Brühl & Weigend, M. (2004). Seed Oil FA of Loasaceae - a New Source of  -Linolenic and Stearidonic Acid. Journal of the American Oil Chemists' Society (JAOCS) 81: 259-263.

Darlington, J. 1934. A monograph of Mentzelia. Ann. Missouri Bot. Gard. 21: 103--226.

Davis W.S., & Thompson, H.J. (1967). A revision of Petalonyx (Loasaceae) with a consideration of affinities in subfamily Gronovioideae. Madroño 19: 1--18.

Dostert, N., & Weigend, M. (1999). A synopsis of the Nasa triphylla complex (Loasaceae), including some new species and subspecies. Harvard Pap. Bot. 4: 439--467.

Gilg, W. (1925): Loasaceae. In: Engler, A. and Prantl, K. (eds.): Die natürlichen Pflanzenfamilien ed. 2., 21: 522--543. Leipzig: W. Engelmann.

Grau, J. (1997). Huidobria, eine isolierte Gattung der Loasaceae aus Chile. Sendtnera 4: 77--93.

Moody, M.L., Hufford, L., Douglas E. Soltis, D.E. & Soltis P.S. (2001). Phylogenetic relationships of Loasaceae subfamily Gronovioideae inferred from matK and ITS sequence data. Amer. J. Bot. 88: 326-336.

Rodríguez-R., E. F. & Weigend, M. (2007). Loasaceae endémicas del Perú. Pp. 391-402 in B. León, J. Roque, C. Ulloa Ulloa, N. Pitman, P. Jørgensen & A. Cano (eds.). El Libro Rojo de las Plantas Endémicas del Perú. Revista Peruana de Biologia Número especial 13 (2): 391-402.

Thompson, H.J., & Ernst, W.R. (1967). Floral biology and systematis of Eucnide (Loasaceae). J. Arnold Arbor. 48: 56-88.

Weigend, M. (2000). 132. Loasaceae. In: Harling, G., Andersson, L. (eds.), Flora of Ecuador  64: 1-92.

Weigend, M. (2001). Loasaceae. In: Bernal, R.  & Forero, E. (eds.): Flora de Colombia Vol. 22: 1-100. Instituto de Ciencias Naturales. Sta Fé de Bogotá.

Weigend, M. (2003). Loasaceae. In: K. Kubitzki & C. Bayer (eds.), The Families and Genera of Vascular Plants 6: 239-254.

Weigend, M. (2003). Loasaceae. In: N. Smith, S.A. Mori, A. Henderson, D.W. Stevenson S.V. & Heald (eds.), Flowering Plants of the Neotropics. Princeton University Press, Princeton, NJ.: 217-219.

Weigend, M. (2004). Four New Species of Nasa ser. Alatae (Loasaceae) in the Amotape-Huancabamba Zone of Peru. NOVON 14: 134-146.

Weigend, M. (2006). Validating subfamily, genus and species names in Loasaceae (Cornales). Taxon 55: 463-468.

Weigend, M. (2007). Systematics of the genus Mentzelia (Loasaceae) in South America, Annals of the Missouri Botanical Gardens 94(3): 655-689.

Weigend, M. & Gottschling, M. (2006) Evolution of funnel-revolver flowers and ornithophily in Nasa (Loasaceae). Plant Biology 8: 120-142.

Weigend, M., Kufer, J., & Mueller, A.A. (2000). Phytochemistry and the systematics and ecology of Loasaceae and Gronoviaceae (Loasales). Amer. J. Bot. 87: 1202-1210.

Weigend, M., T. Henning & Schneider, C. (2003). A revision of Nasa Ser. Carunculatae (Loasaceae subfam. Loasoideae). Systematic Botany 29: 765-781.

Weigend, M., Aitzetmüller, K. & Bruehl, L. (2004). The seeds of Loasaceae subfam. Loasoideae (Cornales) I: Seed release, seed numbers and fatty acid composition. FLORA 199: 424-436.

Weigend, M., Hoot, S., Gottschling, M. & Ackermann, M. (2004). A Preliminary Phylogeny of Loasaceae subfam. Loasoideae Based on trnL(UAA) Sequence Data and its Relation to Systematics and Historical Biogeography. Organisms, Diversity and Evolution 4: 73-90.

Wittmann, D., & Schlindwein C. (1995). Melittophilous plants, their pollen and flower visiting bees in southern Brazil. 1. Loasaceae. Biociências (Porto Alegre) 3: 19-34.

How to cite

Weigend, M. (2009). Neotropical Loasaceae. In: Milliken, W., Klitgård, B. & Baracat, A. (2009 onwards), Neotropikey - Interactive key and information resources for flowering plants of the Neotropics.

Click images to enlarge

Inflorescence of Aosa rupestris from Brazil © Maximilian Weigend, Freie Universität Berlin.

Flower of Blumenbachia hieronymii © Markus Ackermann, Freie Universität Berlin.

Flower of Blumenbachia hieronymii © Markus Ackermann, Freie Universität Berlin.

Inflorescence of Eucnide urens © Markus Ackermann, Freie Universität Berlin.

Flower of Gronovia scandens © Markus Ackermann, Freie Universität Berlin.

Flower of Klaprothia fasciculata © Markus Ackermann, Freie Universität Berlin.

Flower of Loasa acerifolia © Markus Ackermann, Freie Universität Berlin. 

Flower of Loasa nitida © Markus Ackermann, Freie Universität Berlin.

Flower of Mentzelia heterospeala © Maximilian Weigend, Freie Universität Berlin.

Flower of Mentzelia lindleyana © Maximilian Weigend, Freie Universität Berlin.

Flower of Nasa cf. cymbopetala (N. basilica spec. nov. ined.) © Maximilian Weigend, Freie Universität Berlin.

Flower of Nasa carunculata © Maximilian Weigend, Freie Universität Berlin.

Typical indument on shoot of Nasa chenopodiifolia (scabrid and glochidiate and glandular trichomes) © Maximilian Weigend, Freie Universität Berlin.

Apex of stinging hair of Nasa dillonii © Elisabeth Scherer, Freie Universität Berlin.

Stinging hair of Nasa macrothrysa © Elisabeth Scherer, Freie Universität Berlin.

Flower of Nasa poissoniana © Maximilian Weigend, Freie Universität Berlin.

Flower of Nasa ramirezii © Maximilian Weigend, Freie Universität Berlin.

Flower of Nasa urens © Maximilian Weigend, Freie Universität Berlin.

Glochidiate trichomes on stem of Nasa usquiliensis © Maximilian Weigend, Freie Universität Berlin.

Flower of Nasa weigendii © Maximilian Weigend, Freie Universität Berlin.

Ovary of Nasa weigendii, transverse section, with stinging hairs and scabrid trichomes © Elisabeth Scherer, Freie Universität Berlin.

Scabrid trichome from stem of Petalonyx thurberi © Maximilian Weigend, Freie Universität Berlin.

Inflorescence of Plakothira parviflora © Maximilian Weigend, Freie Universität Berlin. 

Flower of Presliophytum heucheraefolium © Maximilian Weigend, Freie Universität Berlin.

Flower of Scyphanthus elegans © Markus Ackermann, Freie Universität Berlin.

Flower of Xylopodia klaprothioides © Maximilian Weigend, Freie Universität Berlin.