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I read the Wikipedia article on Eucalypteae and it doesn't actually say what these plants have in common.

(I am now reading through https://bsapubs.onlinelibrary.wiley.com/doi/pdf/10.3732/ajb.1200025 and I think I've found the answer to this question.)

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  • $\begingroup$ Welcome to Biology.SE. The Biology.SE community has agreed that questions that show little or no prior research effort are off-topic on this site as are "homework" questions unless you have shown your attempt at an answer. Please edit your question and tell us where you've looked for answers, what you do know about the topic, and where exactly you still have questions. Under researched questions may be subject to down-voting and closure. Please take the tour and consult the help center starting with How to Ask for details. $\endgroup$
    – tyersome
    Oct 14 at 19:45
  • $\begingroup$ In particular, what all taxonomic groupings have in common is an ancestor — however, this definitely falls under the category of "trivial to biology professionals" and so is a "homework" question. If that isn't the question you are trying to ask, please edit to clarify what you do want to know and to demonstrate your prior research effort. $\endgroup$
    – tyersome
    Oct 14 at 19:48
  • $\begingroup$ Wouldn't that be all clades? With taxonomic groupings also being on the basis of traits? $\endgroup$
    – Step Start
    Oct 14 at 22:06
  • $\begingroup$ Well, I'd say it is more a matter of inference — what we care about is the evolutionary history. If we were to find that one group of eucalypts had a different ancestor, then those plants would be moved into a new group. The traits (now primarily based on DNA sequences) are the evidence used to determine relatedness — my understanding is morphological traits are now primarily field marks for diagnosing to what group an organism belongs. ——— At any rate, it seems your question is more about common traits, so I think it would be helpful to edit your question's title and body to emphasize that. $\endgroup$
    – tyersome
    Oct 15 at 3:22
  • $\begingroup$ I've edited your title to something that seems clearer to me — please make additional changes if I'm still not understanding you correctly, or if you prefer a different wording. $\endgroup$
    – tyersome
    Oct 15 at 3:28
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It's a slightly tough question that can't be answered with a simple "they share X characteristic in common". It's more that some of them share a characteristic, and some of those share a characteristic with another load of species within the same sub-clade, and some of the characteristics they have are shared with some more... etc. The American Journal of Botany puts it:

(Synapomorphy: a shared trait believed to have been present in a common ancestor.)

Currently, no unambiguous morphological synapomorphies have been confidently identified as defining the Eucalypteae in comparison to other Myrtaceae (however, see Wilson et al., 2001 , for some possibilities). Within the Eucalypteae, however, subclades are defined by synapomorphies. For instance, Angophora Cav., Corymbia , and Eucalyptus share several possible synapomorphies, such as presence of oil glands that protrude above the surface of the epidermis (“emergent oil glands” of Ladiges, 1984 ).

These are modified into distinctive bristle glands in Angophora and Corymbia ( Johnson, 1972 ; Ladiges, 1984 ), which are a unique synapomorphy for the Angophora - Corymbia clade ( Ladiges et al., 1995 ; Wilson et al., 2001 ). Angophora , Corymbia , and Eucalyptus are also characterized by having compound petals and, in Eucalyptus, a portion of the compound petal is usually modified into a staminophore, or stamen-bearing tissue ( Drinnan and Ladiges, 1988 , 1989a , b , 1991a ).

Other characters are apomorphic but are likely homoplasious, having arisen more than once within Eucalypteae. For example, some Corymbia and Eucalyptus species are characterized by the presence of calycine and/or corolline opercula, or cap-like perianth whorls that are deciduous from the flower at or prior to anthesis (e.g., Johnson, 1972 ; Hill and Johnson, 1995 ; Boland et al., 2006 ). Opercula likely have separate origins in these genera ( Ladiges et al., 1995 ; Parra-O. et al., 2009 ). A caducous calyx that usually leaves a scar on the flower bud (see Johnson, 1972 ; Boland et al., 2006 ) is also an apomorphic but homoplastic character within Eucalypteae, being a synapomorphy for a clade within Corymbia ( Ladiges et al., 1995 ; Parra-O. et al., 2009 ) and having arisen at least once on the stem of Eucalyptus subgenus Symphyomyrtus ( Fig. 1B ).

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