science

Praxelinae

Praxelinae is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Praxelinae rather than just read about it. In short: The Praxelinae are a subtribe of the tribe Eupatorieae of the family Asteraceae. Description Species belonging to the subtribe Praxelinae are erect to somewhat sprawling plants that can be either annuals or perennials, herbaceous or subshrubs, and sparsely to densely branched.

Key takeaways

Praxelinae belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Praxelinae to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Praxelinae from memory before moving on to harder problems.

Reference excerpt

The Praxelinae are a subtribe of the tribe Eupatorieae of the family Asteraceae.

Description Species belonging to the subtribe Praxelinae are erect to somewhat sprawling plants that can be either annuals or perennials, herbaceous or subshrubs, and sparsely to densely branched. They never form rosettes when young. Leaves usually arise opposite one another on short to moderately long petioles. Leaf margins can be toothed to toothless, and the blades are not subdivided into leaflets though sometimes taxa in Lomatozona are deeply cut. Leaf shapes range from egg-shaped or oblong, to very slender. In the inflorescences, individual flower heads, or capitula, usually comprise 5-65 florets, whose corollas may be white, blue, lavender or purple.

The main visual feature separating genera of the Praxelinae from genera in other subtribes of the Eupatorieae is that on dried and preserved herbarium specimens, the individual flower heads' involucral bracts are totally deciduous -- they fall off. On living plants the bracts remain hugging the heads' columnar involucre, rather than spreading at maturity, as with members of most other subtribes of the Eupatorieae. Of course this means that in the field this feature doesn't make a good field mark for recognizing species of Praxeliae. Other features characteristic of Praxelinae species, but sometimes shared with species in other subtribes, include: the flower head's receptacle is flat to convex, not conic or columnar; the flowering head's peduncle is not noticeably enlarged just below the head; involucral bracts of similar lengths are arranged in more than two or three spiraling series, and; corolla lobes may bear glands.

Distribution The center of diversity for Praxelinae genera is Brazil. Only two of the subtribe's genera are found outside the country: Certain species of Chromolaena extend north beyond South America and the genus Osmiella is endemic just to Hispaniola.

Taxonomy The subtribe Praxelinae was first published in 1980, in the journal Phylogia. In 2025, a preprint was available online providing evidence based on genetic studies -- Bayesian analysis of ITS -- suggesting that the genus Osmiopsis is a hybrid between the genus Chromolaena (subtribe Praxelinae) and the genus Koanophyllon (subtribe Critoniinae). If this is the case, it the first report of possible inter-subtribal hybridization in the family Asteraceae. Since both taxa occur in the Mexico and Caribbean area, this may support the idea that hybridization has played a significant role in the diversification of the Caribbean flora, as has been shown in species-rich genera from other archipelagos. Taxonomically, it raises the question if sister subtribes Praxelinae and Critoniinae should be united.

Gallery

References

Illustrations

Worked examples

Example 1 — a first encounter with Praxelinae

Start with the simplest possible case. Write down what Praxelinae claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Praxelinae before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Praxelinae ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Praxelinae

In research: Praxelinae appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Praxelinae in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Praxelinae is common in secondary-school and first-year university syllabi. It links to neighbouring topics Eupatorieae, Plant subtribes, so understanding it makes those chapters shorter.
In everyday life: Look for Praxelinae outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Praxelinae in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Praxelinae means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Praxelinae out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Praxelinae in simple terms?

The Praxelinae are a subtribe of the tribe Eupatorieae of the family Asteraceae. Description Species belonging to the subtribe Praxelinae are erect to somewhat sprawling plants that can be either annuals or perennials, herbaceous or subshrubs, and sparsely to densely branched.

Why does Praxelinae matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Praxelinae?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Praxelinae.