Parasitic plant

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About 4,100 species in approximately 19 families of flowering plants are either partly or completely parasitic on other plants Nickrent, D. L. and Musselman, L. J. 2004. Introduction to Parasitic Flowering Plants. The Plant Health Instructor. DOI: 10.1094/PHI-I-2004-0330-01 [link]. Parasitic plants have a modified root, the haustorium, that penetrates the host plant and connects to the xylem or phloem or both. Parasitic plants are characterized as follows:

1a. Obligate parasite - the parasite cannot complete its life cycle without a host.
1b. Facultative parasite - the parasite can complete its life cycle independent of a host.

2a. Stem parasite - the parasite attaches to the host stem.
2b. Root parasite - the parasite attaches to the host root.

3a. Holoparasite - plants that are completely parasitic on other plants and have virtually no chlorophyll.
3b. Hemiparasite - plant that is at least partly photosynthetic but also usually parasitic. Hemiparasites may just obtain water and mineral nutrients from the host plant. Many obtain at least part of their organic nutrients from the host as well.

For hemiparasites, one from each of the three sets of terms can be applied to the same species, e.g.

Nuytsia floribunda is an obligate root hemiparasite.
Yellow rattle is a facultative root hemiparasite.
Mistletoe is an obligate stem hemiparasite.

Holoparasites are always obligate so only two terms are needed, e.g.

Dodder is a stem holoparasite.
Hydnora spp. are root holoparasites.

Plants usually considered holoparasites include broomrape, Cassytha, dodder, Rafflesia, witchweed and Hydnoraceae. Plants usually considered hemiparasites include Castilleja, mistletoe, Western Australian Christmas tree and yellow rattle.

Contents

1 Host range
2 Importance
3 Plants parasitic on fungi
4 References

Host range

Some parasitic plants are generalists and parasitize many different species, even several different species at once. Dodder (Cuscuta spp., Cassytha spp.) and red rattle (Odontites verna) are generalist parasites. Other parasitic plants are specialists that parasitize a few or even just one species. Beech drops (Epifagus virginiana) is a root holoparasite only on American Beech (Fagus grandifolia). Rafflesia is a holoparasite on the vine Tetrastigma.

Importance

Witchweed, broomrape and dodder cause huge economic losses in a variety of herbaceous crops. Mistletoes cause economic damage to forest and ornamental trees.
Mistletoe is a popular Christmas decoration. Kissing under the mistletoe is a Christmas tradition.
Rafflesia arnoldii produces the world's largest flowers at about one meter in diameter. It is a tourist attraction in its native habitat.
Indian paintbrush (Castilleja linariaefolia) is the state flower of Wyoming.
The Oak Mistletoe (Phoradendron leucarpum) is the state flower of Oklahoma.
A few other parasitic plants are occasionally cultivated for their attractive flowers, such as Nutysia and broomrape.
Parasitic plants are important in research, especially on the loss of photosynthesis during evolution.
A few dozen parasitic plants have occasionally been used as food by people Parasitic Angiosperms

Used for Food? [link].

Western Australian Christmas tree (Nuytsia floribunda) sometimes damages underground cables. It mistakes the cables for host roots and tries to parasitize them using its sclerenchymatic guillotine Sclerenchymatic guillotine in the haustorium of Nuytsia floribunda [link].

Plants parasitic on fungi

About 400 species of flowering plants and one gymnosperm, Parasitaxus ustus, are parasitic on mycorrhizal fungi. They are termed myco-heterotrophs rather than parasitic plants. Myco-heterotrophic symbiosis involves three different species, the myco-heterotroph, the mycorrhizal fungus and the autotrophic plant that the fungus is attached to. The myco-heterotroph is indirectly parasitic on the autotrophic plant, which provide organic nutrients to the mycorrhizal fungus. Thus, a myco-heterotroph can also be termed an epiparasite. Some myco-heterotrophs are Indian pipe (Monotropa uniflora), snow plant (Sarcodes sanguinea), underground orchid (Rhizanthella gardneri), bird's nest orchid (Neottia nidus-avis) and sugarstick (Allotropa virgata).

References

[The Parasitic Plant Connection]
[The Strange and Wonderful Myco-heterotrophs]
[Parasitic Flowering Plants]
[The Mistletoe Center]
[Parasitic Plants Biology Study Guide]
[Nickrent, Daniel L. 2002. Parasitic plants of the world.]
[Calladine, Ainsley and Pate, John S. 2000. Haustorial structure and functioning of the root hemiparastic tree Nuytsia floribunda (Labill.) R.Br. and water relationships with its hosts. Annals of Botany 85: 723-731.]
[Milius, Susan. 2000. Botany under the mistletoe: Twisters, spitters, and other flowery thoughts for romantic moments. Science News 158: 411.]
[Hibberd, Julian M. and Jeschke, W. Dieter. 2001. Solute flux into parasitic plants. Journal of Experimental Botany 52: 2043-2049.]

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