Often broomrapes are really challenging as far as their identification is concerned because many related taxa share high similarities as well as they are often highly variable.
This is a brief guide that could allow an easier identification.
Species growing in their proximity. Broomrapes are obligate parasite that feed on other plants and it is known that certain species of broomrapes feed only on certain hosts. Thus, it is important to know which are the species that grow in their proximity since they could be the host.
Habit: it is important to observe the whole plant because the inflorescence:stem ratio may be diagnostic. Some species often show branched stem. Some species usually grow as dense clusters, some others are more aften found as single stems.
Stem: it can be either stout or thinner.
Leaves: they are scale-like and their shape and density can be sometimes useful for the identification.
5.1) Inflorescence shape: it can be either dense or with sparse flowers. Inflorescence apex can be either pointed or more or less rounded and sometimes, due to the presence of lonf bracts, it has a comose appearance.
5.2) Orientation of flowers: it can be either spreading or erecto-patent ot more or less directed upwards.
6.1) Bracts: they can be either longer or shorter than corolla as well as either lanceolate or narrower and more or less linear. In Boulardia latisquama they are particularly large.
6.2) Bracteoles: the genus Phelipanche is characterized by the presence of a pair of narrow bracteoles which are lacking in Orobanche sensu stricto and Boulardia.
Calyx: it is often divided up to the base but in few cases it is entire at base and more or less tubular. It has one or to (exceptionally more) laciniae at each side. The ratio corolla:calyx is often diagnostic. Also the shape of the calyx laciniae is often important since they can be either narrowly triangular or even narrower and subulate.
Corolla. Diagnostic features:
- length (to be measured with millimeter paper)
- upper outline (more or less straight or curved) to be observed from the side
- enlarged at base, with a constriction in the middle, enlarged at apex, narrower close to the apex to be observed from top view
- base: straight, geniculate (bent in lower third) or gradually curved
- outline of the apex: with pointing forward lobes or campanulate to be observed from the side and from top view
- upper lip: pointing forward or upward; entire or emarginate, with entire margin or dentate
- lower lip: pointing forward or downward; with entire margin or dentate, with central lobes larger than the lateral ones or more or less all alike
Stigma: sometimes stigma color may be helpful as well as if it is well exerted from corolla gorge
Stamens. Diagnostic feature such as the point of attachment at corolla is to be measure from corolla base
Hairiness: the kind of hairiness must be observed with attentionj of every part of the plant (e. g. Orobanche pubescens is rather easily distinguished from the related species for the presence of very long hairs on corolla upper side)
Color: also the color of varius parts of the plant must be observed even though broomrapes often show high variability. Anyway, there are species that are never, for example, yellow or other species that always have a blue corolla.
NB: broomrapes that have dried out are extremely difficult to be identified