There are quite a lot of words used to describe plant pathogens that are specific and often difficult to find definitions for. I will try to include any technical vocabulary I use here. The explanations of rust spore stages here are a bit lacking, I'll make a full explainer about the different stages at some point.
Aeciospore
An asexual spore produced in the aecium of a rust. Often orange.
Aecium (pl. aecia)
One of the stages of the rust life cycle. Aecia are usually orange and make asexual aeciospores.
Apothecium (pl. apothecia)
A cup-shaped fruiting body formed by e.g.Leptotrochila.
Biotroph
A pathogen that does not kill its host. Biotrophs have often closely coëvolved with their hosts and are usually quite host-specific.
Coëvolution
The evolution of two species together, each adapting in response to the adaptation of the other.
Coëxistence
[In community ecology] where two or more species can survive an extended period of time together, without one driving the other(s) to extinction. The theory of the set of conditions under which this can occur is coëxistence theory.
Coïnfection
An infection of two different pathogens on the same host plant.
Conidiophore
A structure that holds conidia. A.k.a. conidiosporophore.
Conidium (pl. conidia)
An asexual spore. A.k.a. conidiospore.
Floricolous
Growing on flowers.
Gall
A structure produced by the action of an organism changing the development of its host plant. These structures are for the benefit of the parasite, not the host - the plant's abnormal growth is part of the extended phenotype of the parasite. This word is also used as a verb - the organism galls the host plant.
Generalist
[Of pathogens] infecting a wide range of host plants.
Hemibiotroph
A pathogen that partially kills its host. These are often generalist; one exception is leaf spots like Septoria which usually start out as biotrophs and then switch to killing host tissue when they produce their spores.
Hyperparasite
A parasite of a parasite.
Monophyletic group
The entire group of organisms that descend from a common ancestor. There are no species that descend from that ancestor that are not part of the group. Many genera are like this.
Overdispersion
[In coëxistence theory] the phenomenon where adult plants are further apart than would be expected based on the distribution of seeds.
Paraphyletic group
A group of only some of the organisms that descend from a common ancestor. This is common when some subgroup has evolved a very different lifestyle; for example, fish are a paraphyletic group as land animals (like you!) are also descended from the common ancestor of all fish.
Vertebrates
land animals
some fish
some more fish
Polyphyletic group
A group of composed of multiple, unrelated branches of the tree of life. This is common when a lifestyle has evolved multiple times independently, like flying animals or trees. In the fungi a good example is yeasts — the single-celled lifestyle shows up all over the place.
Seed plants
trees
some herbs
more trees
more herbs
herbs
even more trees
Pustule
This is a rather vague term. A pustule can refer to any raised lump of pathogen tissue growing on the host plant. This can include any stage of a rust (Pucciniales), or the patches of white tissue formed by white rusts (Albuginales).
Pycnidium (pl. pycnidia)
A spherical structure produced by leaf spot fungi. It forms inside the leaf tissue and is packed full of conidia. It eventually forms a pore through which the conidia escape (sometimes at least, I don't know if this is universal).
Specialist
[Of pathogens] infecting a narrow range of host plants.
Synnema (pl. synnemata)
A bundle of conidiophores forming a relatively large column. This is the reproductive structure seen in the genus Phacellium.
Taxon (pl. taxa)
This refers to any level of taxonomy, e.g. species, genus, family. This can include things which haven't been described. For example, if you find something new, you may not know if it is a distinct species or a new subspecies of an existing species. You can refer to it as an undescribed taxon.
Teliospore
Dark brown resting spores produced by rust telia.
Telium (pl. telia)
A rust stage that produces dark brown teliospores.
Vein-delimited
[Of pathogens] restricted to a certain part of the leaf, with leaf veins as the boundary. For example, leaf spots of Septoria aegopodii are vein-delimited:
