Apodanthaceae Tiegh. ex Takht.

Sasaki, D. (2009). Neotropical Apodanthaceae.

Morphology

Description

Herbs, achlorophyllous, endoparasitic. Vegetative body filamentous endophytic tissues within roots and stem of host plant. Stem and leaves absent. Flowers a few mm in diametre, unisexual (plant dioecious ); solitary, in groupings or rows, emerging from the host bark ; bracts in two rows, free or connate . Staminate flowers: tepals 4-5, stamens numerous,  connate into a central column, anthers as several protusions near apex of column, each with just one chamber, dehiscence by a transverse slit, nectary a ring of tissue at base of column and perianth . Carpellate flowers: tepals 4-5, androecium absent (central column present, but anthers absent), ovary inferior or semi-inferior, syncarpous, carpels 4, locule 1, style absent, nectary as in staminate flowers. Fruits berries, irregularly dehiscent ; seeds numerous, small.

General Description

Notes on delimitation

• The family is frequently included in the Rafflesiaceae as a tribe (Apodantheae) or as a distinct family in Rafflesiales. It is considered a taxon of uncertain position by APG (Stevens 2008). Nickrent et al. (2004) suggest affinities with Malvales or Cucurbitales.

Number of genera

• Two: Apodanthes and Pilostyles.

Status

• Both genera are native in the Neotropics.

General notes

• The structures around the flowers are referred to here as bracts, but they have also been called leaves (scale-like), scales or sepals (the inner whorl) by different authors.

Distribution

Distribution in the Neotropics

• Apodanthes Poit.: from Mexico to northern South America.
• Pilostyles Guill.: from Chile and Argentina to Mexico.

Diagnostic

Distinguishing characters (always present)

• Achlorophyllous and endoparasitic plants.
• Vegetative body resembling fungal mycelium (endophytic tissues in host plant).
• Stem and leaves absent.
• Flowers are the only visible part outside the host (solitary, in groups or rows).
• Flowers unisexual and very small, a few mm in diametre, subtended by scalelike bracts.

Key differences from similar families

• The Apodanthaceae differ from other Neotropical holoparasitic families mainly by the absence of well-developed leaves. Hydnoraceae and Balanophoraceae are also leafless holoparasitic families. Hydnoraceae have medium-sized or large bisexual flowers, while Apodanthaceae have very small and unisexual flowers. Balanophoraceae have fungus-like inflorescences, flowers with 1-3 carpels, 1-3 locules and 1 seed per locule.
• Most holoparasitic families are parasitic only on the host roots. The Apodanthaceae are parasitic on aerial parts as well. Cuscutaceae  are parasitic exclusively on the aerial parts. This family includes vines with yellow, orange or red stems, flowers with distinct calyx and corolla and capsular fruits.

Useful tips for generic identification

• Apodanthes is parasitic on plants of the families Salicaceae (Casearia and Xylosma ), some Burseraceae and Meliaceae. The bracts are whitish and yellow to orange, brown or red, free in the inner and outer whorls and connate in the middle ones.
• Pilostyles is parasitic on plants of the family Leguminosae (Astragalus , Dalea , Daviesia , Mimosa ). The bracts are red to brown and free.

Literature

Important literature

Heywood, V.H. 2007. Apodanthaceae. In: Heywood, V.H., Brummit, R.K., Culham, A. & Seberg, O. (eds.). Flowering Plant Families of the World,  pp. 272-274. Royal Botanic Gardens, Kew.

Mitchell, J.D.T. 2004. Rafflesiaceae. In: N. Smith, S.A. Mori, A. Henderson, D.W. Stevenson & S.V. Heald (eds.). Flowering Plants of the Neotropics, pp. 318-319. New York Botanical Garden & Princeton University Press, Princeton.

Nickrent, D.L., Blarer, A., Qiu, Y.-L., Vidal-Russell, R. & Anderson F.E. 2004. Phylogenetic inference in Rafflesiales: the influence of rate heterogeneity and horizontal gene transfer. BMC Evol. Biol. 4: 40.

Stevens, P.F. 2008. Angiosperm Phylogeny Website, version 9. http://www.mobot.org/MOBOT/research/APweb/.