Can two different species in the same genus generally succeed in the same habitat?

Question

This plant-care website writes

In the context of plant care, usually most plants within the same genus need the same environmental conditions suitable for plant growth. If the genus of a plant is known, the information can be used to apply the appropriate levels of plant care.

I'm wondering if this is true in general. A more general question would be, if I know that two species are in the same genus, what phenotypical similarities will they have?

So far I've only found that genus classification is based on genetic similarity, but that doesn't say anything about what phenotypical similarities there may be between different species in the same genus.

Answer 1

It is not correct to say that genera are based on genetic similarity. Different lineages diverge genetically at highly variable rates, and there is no set cut-off for what defines a genus. Instead, genera are based on publications, which could be over 100 years old. Genera are not a biologically real category the way species are, so one genus may hold hundreds of species, while another, only one. Most of these genera were defined before molecular data was possible. There are no set phenotypic criteria for the definition of a genus, except that a well-described genus should have at least one fixed character that defines it. So in answer to your question, yes, two species in the same genus (congeners) will often exist in the same habitat. There would be selective pressures to separate them in terms of the niche that they occupy. The publication you referred to is simply a best guess: if you don't have information on the habitat requirements of a species, it would most likely share many similarities with its close relatives. Phylogeny is predictive, but different species in the same genus need not be identical in terms of their ecological requirements.

Answer 2

I don't think you can generalize either way. For an example, take penstemons: https://en.wikipedia.org/wiki/Penstemon Hereabouts I can find 3 or 4 species growing in the same conditions, within a radius of 3-4 m. I can also find other species growing in close proximity but very different conditions, e.g. wet meadow vs dry, rocky slope.