Orobanchaceae Vent

This description applies only to the parasitic Scrophulariaceae, not to autotrophic members. The components here considered part of this group are: Aegineticeae Livers., Antirrhineae (Antirrhinaceae) DC. & Duby, Orobanchaceae Vent., Pediculares (Pedicularidaceae) Juss., Phelypaeaceae Horan, Rhinanthoideae (Rhinanthaceae) Vent., Scrophulariaceae Juss., and Syndiaspermaceae Dulac.

Parasitic Genera Included:*Aeginetia L., Agalinis Raf. (including Anisantherina Pennell), Alectra Thunb. (including Pseudorobanche Rouy.), Ancistrostylis T.Yamaz., Aureolaria Raf., Bartsia L., *Boschniakia C. Meyer ex Bong., Buchnera L., Bungea C.A.Mey, Buttonia Benth., Castilleja Mutis ex L. f. , Centranthera R.Br. (including Razumovia Spreng.), *Christisonia Gardner (including Campbellia Wight), *Cistanche Hoffsgg. & Link., Clevelandia Greene (formerly Orthocarpus), *Conopholis Wallroth., Cordylanthus Nutt. ex Benth. (including Adenostegia Benth.), Cycniopsis Engl. , Cycnium E. Meyer ex Benth., Dasistoma Raf. , *Epifagus Nutt. , Escobedia Ruiz & Pav. , Esterhazya J.C.Mikan. , Euphrasia L., Gerardiina Engl., Ghikaea Volkens & Schweinf., *Gleadovia Gamble & Prain., Graderia Benth. (including Bopusia C.Presl.), *Harveya Hook. , Hedbergia Molau (related to Bartsia), *Hyobanche L. , * Kopsiopsis (Beck) Beck (formerly Boschniakia), *Lathraea L. , Leptorhabdos Schrenk. , Lesquereuxia Boiss. & Reut., Leucosalpa Scott-Elliot. , Macranthera Nutt. ex Benth. , Magdalenaea Brade. , *Mannagettaea H. Sm. , Melampyrum L. , Melasma P. Bergius. , Micrargeria Benth. , Micrargeriella R.E.Fr. , Monochasma Maxim. ex Franch. & Sav., *Necranthus Gilli. , Nothochilus Radlk. , Odontites Ludw. (including Orthantha (Benth.) Wettst.; Orthanthella Rauschert), Omphalotrix Maxim. , Ophiocephalus Wiggins, *Orobanche L. (including Aphyllon Mitch), Orthocarpus Nutt., Parastriga Mildbr., Parentucellia Viv., Pedicularis L. , Petitmenginia Bonati. , *Phacellanthus Siebold & Zucc. , *Phelypaea L. , Phtheirospermum Bunge ex Fisch. & C.A.Mey. (including Centrantheropsis Bonati )., Physocalyx Pohl., *Platypholis Maxim. , Pseudobartsia D.Y.Hong. , Pseudosopubia Engl. , Pseudostriga Bonati. , Pterygiella Oliv. , Radamaea Benth. , Rhamphicarpa Benth., Rhaphispermum Benth. , Rhinanthus L. , Rhynchocorys Griseb., Schwalbea L. , Seymeria Pursh. , Silviella Pennell (including Silvia Benth.), Siphonostegia Benth. , Sopubia Buch.-Ham. ex D. Don., Spirostegia Ivanina. , Striga Lour. Ca. , Tetraspidium Baker., Thunbergianthus Engl., *Tienmuia Hu. , Triphysaria Fischer & C. Meyer (formerly Orthocarpus) , Tozzia L. , Vellosiella Baill. , Xizangia D.Y.Hong (=Xixangia), *Xylanche G. Beck. , Xylocalyx Balf.f. ,

Those genera marked with an asterisk (*) have traditionally been placed in Orobanchaceae s. str.

Habit: Annual, biennial, and perennial herbs sometimes with glandular trichomes or hairs with basal cystoliths (e.g. Striga); may produce orobanchin and iridoid compounds that cause the leaves to turn black upon drying. Holoparasites tending toward succulence.

Parasitism: Both hemiparasites and holoparasites occur in this family. The former are photosynthetic plants that obtain water and dissolved nutrients via haustorial connections to their host roots. The holoparasites (many of which were formerly classified in Orobanchaceae) are nonphotosynthetic and obtain not only water and nutrients from their hosts but also organic compounds from the phloem.

Roots: Some of the more advanced parasites such as Striga and Orobanche produce primary haustoria that result from a direct transformation of the apex of the seedling radicle. Later, lateral (secondary) haustoria may may form along the root. See "Haustorial Initiation in Agalinis" for a photographic documentation of haustorial development. A recent review of haustorial initiation and differentiation was written by Riopel and Timko (1995, Chapter 3 In: M. C. Press and J. D. Graves, Parasitic Plants, Chapman and Hall).

Stem: Nodes unilacunar. Primary vascular tissue comprising a ring of bundles, or in two or more rings of bundles; centrifugal. Interxylary phloem absent. Secondary thickening developing from a conventional cambial ring. Xylem with or without fiber tracheids but with vessels; parenchyma if present, apotracheal, or paratracheal (usually very sparse or absent). Sieve-tube plastids S-type. Pith with or without diaphragms.

Leaves: Alternate, opposite or spiralled; petiolate to sessile, without stipules; in Seymeria, finely divided (pinnatifid or bipinnatifid) into filiform segments; in the holoparasites reduced to fleshy spiral scales. Venation pinnate or palmate. Stomata anomocytic, or anisocytic, confined to one or both surfaces;

Inflorescence: Spikes and racemes common.

Plant Sex: Plants hermaphrodite. Insect pollinated; some autogamous (e.g. Striga asiatica).

Flowers: Generally bracteate (one flower per bract). In Castilleja, the calyx and corolla are highly modified (often yellow or green) and the subtending bract is the colorful pollinator attractor.

Calyx: synsepalous of two to five sepals, actinomorphic to zygomorphic, often deeply 4- to 5-lobed.
Corolla: sympetalous, zygomorphic to nearly actinomorphic (e.g.
Buchnera), bilabiate in some. Lobes commonly five, imbricate or valvate with the median member posterior.
Nectary: from an annular hypogynous disk.
Androecium: epipetalous, alternate with corolla lobes. Stamens 4 or 5, equal or unequal. A sterile staminode may be present (then the posterior median member) or absent. Anthers tetrasporangiate and dithecal (unithecal in Buchnera), introrse, opening by longitudinal slits or pores (some Euphrasia); pollen binucleate or trinucleate (Euphrasia), tricolporate.
Gynoecium: superior (hypogynous), syncarpous of two (rarely three) carpels, bilocular or unilocular (this character has been used to separate Scrophulariaceae from Orobanchaceae); with one style; stigma 1- to 2-lobed.
Ovule: numerous (tens to hundreds) and present on axile placentas, anatropous, hemitropous or campylotropous, tenuinucellar with single integument and a tapetum that is open at the micropylar end.
Embryo, etc.: Undifferentiated in many taxa; endosperm development cellular, endosperm haustoria present.

Fruit: Usually a septicidal capsule. Dispersal of seeds from the capsule of Pedicularis occurs by movement induced by rain drops.

Seed: Small to minute (e.g. Orobanche, Striga), exotestal (an ornamented outer layer - see Castilleja sessiliflora picture); endosperm oily. Seedling germination cryptocotylar in holoparasites.

Chromosomes: X = 6, 12, 18-21.

Link to Description in Delta (Scrophulariaceae)

Link to Description in Delta (Orobanchaceae)


SIUC / College of Science / Parasitic Plant Connection / Scrophulariaceae
URL: http://www.parasiticplants.siu.edu/Scrophulariaceae/description.html
Last updated: 15-May 06/ dln