Neotropical Linaceae

Ricardo de S. Secco

Museo Goeldi, Belem, Para, Brazil.

Description

Annual or perennial herbs, shrubs or trees.  Leaves simple, alternate or opposite, petiolate or sessile, with deciduous stipules or exstipulate, these sometimes modified into glandsInflorescences racemes, panicles, terminal spikes or axillary fascicles.  Flowers bisexual, actinomorphic; sepals 4-5, free or partially fused at base, imbricate; petals 5, free, irregular, with or without appendages at base; stamens 5-15, iso- or diplostemonous, with filaments fused at base, anthers longitudinally dehiscent, introrse; staminodes sometimes present; ovary superior, 2-5-locular, ovules (1-)2 per locule, style 1-3-5-fid, free or forming a column, stigma sometimes capitateFruit drupaceous, indehiscent or septicidal capsuleSeeds alate or not, endosperm abundant, scarce or absent, embryo straight with flattened cotyledons.

Notes on delimitation

  • The position of Linaceae in the Malphigiales clade is still controversial as are the relationships among the genera considered part of the Hugoniaceae and the Linaceae s.s.  According to Cronquist (1988), the neotropical genera Hebepetalum Benth. and Roucheria Planch. should be included in the Hugoniaceae, while the APG II (2003), APG III (2009), McDill & Simpson (2011) place these two genera in the Linaceae subfamily Hugoniaceae together with three Old World genera.
  • Ochthocosmus Benth. (seven species) and Cyrillopsis Kuhlm. (two species) traditionally belonged to the Linaceae, but according to Ramirez & Berry (1999), Ramirez & Secco (2008), and APG III (2009) they are currently placed in Ixonanthaceae.

Distribution in the Neotropics

  • According to Ramirez & Berry (1999) and Secco (2008, 2010) three species of Hebepetalum, seven of Roucheria, six of Linum (some cultivated) and one of Cliococca occur in the Neotropics. 
  • Kearns (2004) cited ca. 45 species of Linum occuring throughout the New World tropics and subtropics.
  • Rogers (1968) recognised 14 species of Linum in Central America.

Distinguishing characters (always present)

  • Herbs (Linum and Cliococca), shrubs or trees (Hebepetalum and Roucheria).
  • Simple leaves, usually alternate, sometimes opposite (Linum).
  • Sepals and petals 5; stamens 5-15; ovary superior.
  • Fruits drupaceous (Hebepetalum and Roucheria) or septicidal capsules (Linum and Cliococca).

Other important characters

  • Oily seeds present in Linum.

Key differences from similar families

1.   Stamens up to 5, presence of intrastaminal disc; petals imbricate, persistent in fruit …. Ixonanthaceae
1.   Stamens 5-120; absence of intrastaminal disc; petals absent in fruit …. 2

2.   Absence of balsamic oils and resins in the bark and fruit; stamens up to 15; connective not thickened, anther thecae normal; absence of ovary disc …. Linaceae
2.   Presence of balsamic oils and resins in the bark and fruit; stamens 10-120; connective thickened, anther thecae minute; presence of ovary disc …. Humiriaceae

Number of genera

Linaceae comprises four genera in the Neotropics:

  • Cliococca Bab. - 1 spp.,
  • Hebepetalum Benth. - 3 spp.,
  • Linum L. (ca. 187 species in total, c. 45 in the New World tropics and subtropics).
  • Roucheria Planch. - 7 spp.

Useful tips for generic identification

Key to the genera of Neotropical Linaceae

1.   Shrubs or trees; stamens 10 or more; fruit drupaceous …. 2
1.   Herbs; stamens 5; fruit a septicidal capsule …. 3

2.   Leaf venation reticulate; flowers with densely barbate petals internally, base unguiculate …. Hebepetalum
2.   Leaf venation with numerous parallel secondary veins; flowers with glabrous petals internally, base not unguiculate …. Roucheria

3.   Plants with subterranean rhizomes; petals imbricate, white or pale pink, smaller than sepals; ovary with complete false septa; fruit indehiscent; mature seeds enclosed by carpels when released …. Cliococca
3.   Plants without subterranean rhizomes; petals convolute, yellow, blue or red, larger than sepals; ovary with incomplete false septa; fruit dehiscent; mature seeds free when released …. Linum

Notable genera and distinguishing features

  • In the Neotropics the most notable genera are speceis of Hebepetalum and Roucheria, found as trees or shrubs most frequently in forests.  Roucheria is easily identified by its leaves with closely spaced, parallel venation, whereas Hebepetalum is distinguished by the leaves with typically reticulate venation.
  • Cliococca and Linum are herbs, but the former has subterranean rhizomes and the latter does not. Moreover, Linum flowers are more showy with convolute yellow, blue or red petals, which are larger than the sepals.

Status

  • In the Neotropics Linaceae consists of native (Hebepetalum, Roucheria and Linum), endemic (Linum, Hebepetalum and Roucheria), and cultivated (Linum and Cliococca) species.

General notes

  • Amongst Linaceae, Linum usitatissimum L. is the species of greatest economic interest, as a source of fibre from the stem (linen), for medicinal uses and as a food source (linseed, and flax oil and seed).
  • Record & Hesse (1949) mentioned that the woods of Hebepetalum and Roucheria are hard and heavy, and therefore are probably not significantly attacked by insects, and are of good durability.

Important literature

APG II. 2003. An update of the Angiosperm Phylogeny Group classification for the orders and families of flowering plants: APG II. Botanical Journal of the Linnean Society 141: 399-436.

APG III. 2009. An update of the Angiosperm Phylogeny Group classification for the orders and families of flowering plants: APG III. Botanical Journal of the Linnean Society 161: 105-121.

Hooren, A.M.N. van & Nooteboom, H.P. 1984. Linaceae and Ctenolophonaceae of Malesia with notes on their demarcation and the relationships with Ixonanthaceae. Blumea 29: 547-563.

Kearns, C.A. 2004. Hugoniaceae, Linaceae.  In: Smith, N., Mori, S.A., Henderson, A., Stevenson, D.W. and Heald, S.V. (eds.). Flowering Plants of the Neotropics, pp. 184-185; 215-216. The New York Botanical Garden, Princeton University Press, Princeton.

Macbride, J.F. 1949. Linaceae. In: J.F. Macbride (ed.) Flora of Peru. Field Mus. Nat. Hist., Bot. ser. 13, part 3(2): 621-633.

McDill, J. & Simpson, B.B. 2011. Molecular phylogenetics of Linaceae with complete generic sampling and data from two plastid genes. Bot. J. Linnean Soc. 165: 64-83.

Mildner, R.A. & Rogers, C.M. 1978. Revision of the native South American species of Linum (Linaceae). Phytologia 39: 343-390.

Ramirez, N., Berry, P.E. & Jardim, A. 1999. Hugoniaceae, Ixonanthaceae. In: Steyermark, J.A., Berry, P.E., Yatskivych, K. and Holst, B.K. (eds.), Flora of the Venezuelan Guayana, vol. 5, pp. 618-623; 664-671. Missouri Botanical Garden Press, St. Louis.

Ramirez, N. & Secco, R.S. 2008. Hugoniaceae, Ixonathaceae. In: Hokche, O., Berry, P.E. & Huber, O. (Eds). Nuevo Catálogo de la Flora Vascular de Venezuela, pp. 418-419; 422-423. Fundación Instituto Botánico de Venezuela.  Dr. Tobias Lasser, Caracas.

Record, S.J. & Hesse, R.W. 1949. Timbers of the New World. New Haven, Yale University, 640 pp.

Rogers, C.M. 1968. Yellow-flowered species of Linum in Central America and Western North America. Brittonia 20 (2): 107-135.

Rogers, C.N. & Smith, L.B. 1975. Lináceas. In: Reitz, R. (ed.), Flora Ilustrada Catarinense. fasc. LINA: 3-34. Herbário Barbosa Rodrigues, Itajaí, Santa Catarina.

Secco, R.S. 2008. Linaceae. In: Hokche, O., Berry, P.E. & Huber, O. (Eds). Nuevo Catálogo de la Flora Vascular de Venezuela, p. 670. Fundación Instituto Botánico de Venezuela.  Dr. Tobias Lasser, Caracas.

Secco, R.S. & S.M.B. Silva. 1990. Materiaes para  a Flora Amazônica- VIII. Contribuição à sistemática de Linaceae da Amazônia Brasileira. Bol. Mus. Para. Emilio Goeldi, série Botânica 6(1): 113-135.

Sothers, C.A.; J.M. Brito & R.S. Secco. 1999. Hugoniaceae. In Ribeiro, J.E.L. et al. (editors), Flora da Reserva Ducke. Manaus, INPA/DFID. p. 504.

Steyermark, J.A. & J.L. Luteyn. 1980. Revision of the genus Ochthocosmus (Linaceae). Brittonia 32 (2): 128-143.

How to cite

Secco, R. de S. (2012). Neotropical Linaceae. In: Milliken, W., Klitgård, 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/Linaceae.htm.