Orobanchaceae is the largest of the 20–28dicot families that express parasitism.[10] Apart from a few non-parasitic taxa, the family displays all types of plant parasitism:facultative parasite,obligate parasite, hemiparasites, and holoparasites.
Parasitic plants are attached to their host by means ofhaustoria, which transfernutrients from the host to the parasite. Only the hemiparasitic species possess an additional extensive root system referred to as the lateral or side haustoria. In most holoparasitic species there is a swollen mass of short, bulky roots or one big swollen haustorial organ, which may be simple or composite, commonly called the terminal or primary haustorium.[11]
Plants are reduced to short vegetative stems, their alternate leaves are reduced to fleshy, tooth-like scales, and have multicellular hairs interspersed with glandular hairs.[12]
The hemiparasitic species (transferred from Scrophulariaceae) with green leaves are capable of photosynthesis, and may be either facultative or obligate parasites.
Thehermaphroditic flowers are bilaterally symmetrical and grow either inracemes or spikes or singly at the apex of the slender stem. The tubularcalyx is formed by 2–5 united sepals. There are five united, bilabiatepetals forming thecorolla and they may be yellowish, brownish, purplish, or white. The upper lip is two-lobed, the lower lip is three-lobed. There are two long and two shortstamens on slender filaments, inserted below the middle, or at the base of the corolla tube, alternating with the lobes of the tube. A fifthstamen is either sterile or lacking completely. Theanthers dehisce via longitudinal slits. Thepistil is one-celled. The ovary is superior. The flowers arepollinated by insects or birds (e.g.,hummingbirds, as inCastilleja).
Thefruit is adehiscent, non-fleshy, 1-locularcapsule with many very minute endospermicseeds. Fruits of Orobanchaceae are small and abundant and can produce between 10,000–1,000,000 seeds per plant.[13] These are dispersed by the wind over long distances, which increases their chances of finding a new host.
The taxon was first described in 1799 byÉtienne Pierre Ventenat as Orobanchoideae. The family name Orobanchaceae is aconserved name.[14][15] Despite the similar morphological traits found in bothScrophulariaceae and Orobanchaceae, the latter is now considered a separate monophyletic taxon, on both molecular and mophological grounds. The 2016APG IV system expanded Orobanchaceae to include genera previously placed in Scrophulariaceae, so that the family absorbed the former Lindenbergiaceae and Rehmanniaceae.[16] These two former families may be treated as tribes.[17]Molecular phylogenetic studies show that they are sisters to the other Orobanchaceae genera:[18][19]
Development of the haustoria was a significant evolutionary event that allowed for the advancement ofparasitic plants. The holoparasitic clade,Orobanche, delineates the first transition from hemiparasitism to holoparasitism within Orobanchaceae.[citation needed]
Plastid genes group all parasitic members of the Orobanchaceae, both hemiparasitic and holoparasitic, into a single monophyletic clade.[12] This phylogenetic relationship supports both the merging of the hemiparasitic members of the Scrophulariaceae with the Orobanchaceae, and also the hypothesis of one origin of hemiparasitism within the family, making it a key trait for delimiting clades and reconstructing evolutionary history. More recent phylogenetic analyses looking at nuclear orthologous genes across the major lineages of the Orobanchaceae have led to a highly resolved phylogeny that confirms these previous findings, adding that the common ancestor for parasitic species within the Orobanchaceae appeared approximately 38.6 million years ago.[20]
Once this parasitic habit evolved, holoparasitism is thought to have arisen several times independently, although the exact number is the subject of some debate.[4][12] The plastid gene study, Young et. al (1999), states that holoparasitism evolved five times in different lineages: Once fromHarveya,Lathraea and the traditional Orobanchaceae as well as the genusAlectra and the genusStriga. Importantly, more recent studies have found three origins of holoparasitism, with the origin at the genusAlectra belonging to the same lineage as that ofHarveya, andStriga sometimes considered a hemiparasite as some species conduct photosynthesis for parts of their life cycles.[4] These independent origins of holoparasitism illustrate homoplastic traits within a monophyletic group and highlight that while parasitism does act as a unifying trait for parts of the Orobanchaceae, it is a much more complex feature than originally thought. The repeated evolution of complete reliance on parasitism has significant impacts for understanding the mechanisms behind Orobanchaceous diversification.
This pattern of the evolution of holoparasitism does not support previous systematic conclusions based on the idea of an evolutionary series throughout the hemiparasitic to holoparasitic genera of the Scrophulariaceae and the Orobanchaceae.[12] Rather, these new conclusions emphasize the role that parasitism plays on diversification within the Orobanchaceae, highlighting the fact that different parasitic lineages arose in different evolutionary contexts, and that the internal systematics of the Orobanchaceae can be better understood as multiple branching points of differentiation rather than a linear gradient leading to one form of parasitism.
The parasitism and its different modes have been suggested to have an impact ongenome evolution, with increasedDNA substitution rates in parasitic organisms compared to non-parasitic taxa.[21] For example, holoparasite taxa of Orobanchaceae exhibit fastermolecular evolutionary rates than confamilial hemiparasites in threeplastid genes.[22]
As of February 2025[update],Plants of the World Online accepted 99 genera.[3] Three further genera are accepted by other sources, and are included in the following list.
The family Orobanchaceae has acosmopolitan distribution, found mainly intemperateEurasia, North America, South America, parts of Australia, New Zealand, and tropical Africa. The only exception to its distribution is Antarctica, though some genera may be found insubarctic regions.[25]
This family has tremendous economic importance because of the damage to crops caused by some species in the generaOrobanche andStriga. They often parasitize cereal crops likesugarcane,maize,millet,sorghum, and other major agricultural crops likecowpea,sunflower,hemp,tomatoes, andlegumes. Because of the ubiquitous nature of these particular parasites in developing countries, it is estimated to affect the livelihood of over 100 million people, killing 20 to 100 percent of crops depending on infestation.[26]
Some genera, especiallyCistanche andConopholis, are threatened by human activity, includinghabitat destruction and over-harvesting of both the plants and their hosts.
Research for this plant family can often be difficult due to its permit requirements for collection, travel, and research.
^Tank, David C.; Wolfe, Andrea; Mathews, Sarah; Olmstead, Richard G. (2020-04-30). "Orobanchaceae E. P. Ventenant 1799:292 [D. C. Tank, A. D. Wolfe, S. Mathews, and R. G. Olmstead], converted clade name". In de Queiroz, Kevin; Cantino, Philip D.; Gauthier, Jacques A. (eds.).Phylonyms: A Companion to the PhyloCode. CRC Press. pp. 1749–1751.ISBN978-0-429-82120-2.
^Kebab, E. (2013). Joel, Daniel M.; Gressel, Jonathan; Musselman, Lytton J. (eds.).Parasitic orobanchaceae parasitic mechanisms and control strategies. Berlin: Springer.ISBN978-3-642-38146-1.
^Ventenat, É. P. (1799)."Les Orobanchoïdes, Orobanchoideae".Tableau du règne végétal, selon la méthode de Jussieu. Vol. 2. Paris: de l'Imprimerie de J. Drisonnier. pp. 292–295. Retrieved2025-02-28.
^Stevens, P.F. (2001 onwards)."Orobanchaceae". Angiosperm Phylogeny Website. Retrieved 2025-02-28.
^Li, Xi; Feng, Tao; Randle, Chris & Schneeweiss, Gerald M. (2019). "Phylogenetic Relationships in Orobanchaceae Inferred From Low-Copy Nuclear Genes: Consolidation of Major Clades and Identification of a Novel Position of the Non-photosyntheticOrobanche Clade Sister to All Other Parasitic Orobanchaceae".Frontiers in Plant Science.10 902.Bibcode:2019FrPS...10..902L.doi:10.3389/fpls.2019.00902.PMC6646720.PMID31379896.
^Xu, Yuxing; Zhang, Jingxiong; Ma, Canrong; Lei, Yunting; Shen, Guojing; Jin, Jianjun; Eaton, Deren A. R.; Wu, Jianqiang (2022). "Comparative genomics of orobanchaceous species with different parasitic lifestyles reveals the origin and stepwise evolution of plant parasitism".Molecular Plant.15 (8):1384–1399.Bibcode:2022MPlan..15.1384X.bioRxiv10.1101/2022.04.13.488246.doi:10.1016/j.molp.2022.07.007.
^Westwood, James H.; dePamphilis, Claude W.; Das, Malay; Fernández-Aparicio, Mónica; Honaas, Loren A.; Timko, Michael P.; Wafula, Eric K.; Wickett, Norman J.; Yoder, John I. (April–June 2012). "The Parasitic Plant Genome Project: New Tools for Understanding the Biology ofOrobanche andStriga".Weed Science.60 (2):295–306.Bibcode:2012WeedS..60..295W.doi:10.1614/WS-D-11-00113.1.ISSN0043-1745.S2CID26435162.
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