Family: Broomrape [Orobanchaceae]










A great many Figwort Family Genus [Scrophulariaceae] have recently been moved by taxonomists to other Families. Many, but not all, have been moved into either the Plantain [Plantaginaceae] or the Broomrape [Orobanchaceae] Families.

The following Genera have moved from the Figwort Family to the Broomrape Family [Orobanchaceae]:
Bartsia, Euphrasia, Melampyrum, Odontites, Parentucellia, Pedicularis and Rhinanthus.

[EUPHRASIA] Eyebrights


Hybrid Chart: EYEBRIGHTS (larger)

A triple hybrid exists, namely:
Euphrasia confusa × frigida × scottica
which is over-lapped on the above chart by normal hybrids.

(Euphrasia arctica subsp. arctica) Eyebright
(Euphrasia arctica subsp. borealis) Arctic Eyebright
(Euphrasia officinalis agg.) Eyebright
(Euphrasia officinalis subsp. anglica) English Eyebright
(Euphrasia officinalis subsp. monticola) Eyebright
(Euphrasia officinalis subsp. pratensis) Eyebright
(Euphrasia rhumica)

[MELAMPYRUM] Cow-wheats

Common Cow-wheat. (Melampyrum pratense) Photo: © RWD

Field Cow-Wheat (Melampyrum arvense) Photo: © Dawn Nelson

[ODONTITES] Bartsias

Red Bartsia. (Odontites vernus) Photo: © RWD

[PARENTUCELLIA] Yellow Bartsia

Yellow Bartsia (Parentucellia viscosa) Photo: © RWD

[BARTSIA] Alpine Bartsia

Alpine Bartsia (Bartsia alpina) Photo: © Dawn Nelson

[RHINANTHUS] Yellow-rattles

Yellow Rattle. (Rhinanthus major) Photo: © RWD

[PEDICULARIS] Louseworts

Lousewort (Pedicularis sylvatica) Photo: © RWD

Marsh Lousewort (Pedicularis palustris) Photo: (CC by 2.0) Geoff Toone

[OROBANCHE] Broomrapes

Broomrapes are parasitic plants that are totally incapable of photosynthesising themselves because they completely lack chrorophyll. Instead they parasitise other plants, which then become their host, such as Ivy, Greater Knapweed, Pea Family plants, Bedstraws, etc, sometimes from a surprising separating distance. It turns out that differing Broomrapes parasitise these plants; thus Knapweed Broomrape parasitises Greater Knapweed, Bedstraw Knapweed parasitises Bedstraw, etc, etc, and they all look slightly different, some slightly blue, others golden, or honey coloured, or purple, and various physical characteristics are also slightly different.

Moreover, many species of Broomrape have a plethora of differing colour-forms. These colour-forms are forma, a generic term which is below sub-species rank and applied mainly to colour varieties (and only occasionally to single-difference variations). Many plants seem to possess colour variations but the colour differences are usually masked by the strong green colour of the chlorophyll within most plants. However, Broomrapes entirely lack chlorophyll, so there is no masking of colour variations, which is possibly why most species seem to have over a dozen differing colour-forms. [However, Clive Stace makes no mention of these colour-differentiated forma in Broomrapes]. Some species of Broomrape have just one photosynthesising host plant which they parasitise exclusively, a differing plant for each Broomrape species. But some Broomrapes seem not so fussy and will parasitise a number of differing photosynthetic plants.

The Author wonders if all (or maybe most) Broomrapes start off the same, and then acquire their particular characteristics after parasitising their prey? So Ivy Broomrape acquires the characteristics of Ivy Broomrape because it has parasitised Ivy, but should it instead have parasitised Greater Knapweed then it will look like Knapweed Broomrape. This idea is probably incorrect.

The Author is not a qualified biologist, so this idea should be taken with a large pinch of salt, but he would point out that since Broomrape lacks a rhizome and some other key characteristics of plants (such as chlorophyll), then it may be acquiring more from its host than just nutrients. And those extra components in the 'nutrients' will include many widely different secondary metabolites from the host plant which are totally alien to Broomrapes. These unique secondary metabolites may be influencing how any particular Broomrape grows, for instance its colour and shape. And it may not only be secondary metabolites which are in the nutrients extracted from the host plant, some genetic material from the host could conceivably in there too. Tiny snippets of RNA or DNA for instance, or even whole genes, although whether any is expressed is another matter. Or perhaps the host has found some way of modulating the methylation / acetylation / phosphorylation of the Broomrapes' genes, thereby altering their expression - through a process called  epigenetics. And then there are the signalling molecules, which can travel both through the air and through the soil. Signalling molecules are known to play a large role in certain aspects of plants, but their study has hardly begun.

Your Author does not think that it is a coincidence that Yarrow Broomrape is a striking blue colour. Yarrow contains many Azulenes (Azulene is a hydrocarbon with identical empirical formula to that of Naphthalene (C10H8) - which has two aromatic 6-membered carbon rings fused on one edge) whereas Azulene has a 5-membered ring fused to a 7-membered ring. But whereas Naphthalene is colourless, Azulene is a striking blue. Your Author thinks Yarrow Broomrape obtains its blue coloration from the Azulene within Yarrow.

The Author thinks a great deal lies undiscovered about how Broomrapes utilise the 'nutrients' obtained from their host(s) and how it may influence their development.

Common Broomrape (Orobanche minor) Photo: © RWD

Thyme Broomrape (Orobanche alba) Photo: © Paula O'Meara

Knapweed Broomrape (Orobanche elatior) Photo: © Dawn Nelson

Greater Broomrape (Orobanche rapum-genistae) Photo: (CC by 2.0) Geoff Toone

Yarrow Broomrape (Orobanche purpurea) Photo: (CC by 2.0) Geoff Toone

Oxtongue Broomrape (Orobanche picridis) Photo: (CC by 2.0) Geoff Toone

Ivy Broomrape (Orobanche hederae) Photo: (CC by 2.0) Geoff Toone

[LATHRAEA] Toothworts

The Toothworts lack chlorophyll so are completely unable to photosynthesise and must obtain their nutrients by parasitizing the roots of a host plant. The hosts of Toothwort itself are Hazel and Alder, but sometimes on Beech. It occupies shady places like hedges. Toothwort is also a  borderline carnivorous plant, meaning that it can physically trap insects but only might be capable of digesting them and absorbing the nutrients, or partially absorbing them. Obviously, the more means it has at its disposal for obtaining nutrients the better, and maybe carnivory is just supplementary until it can parasitise a nearby plant for a more reliable supply of nutrients.

Purple Toothwort (Lathraea squamaria) Photo: © Sue King-Smith

Toothwort (Lathraea squamaria) Photo: © Colin Martin

Family: Broomrape [Orobanchaceae]

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