A research article is a primary source.
It reports the methods and results of an original study. The authors collect and analyze raw data and draw conclusions from the results of that analysis.
Research papers follow a particular format. They include:
An introduction: This will often include a review of the existing literature on the topic, and explain the rationale of the authors’ study. It demonstrates that the authors are aware of existing studies, and are planning to contribute to this existing body of research.
A methods section: The authors describe how they collected and analyzed data. Statistical analyses are included.
A results section: This describes the outcomes of the data analysis. Charts and graphs illustrating the results are typically included.
A discussion: The authors explain their results and theorize on their importance to existing and future research.
References: This is a list of sources that the authors used to plan their study and support their discussion.
Note the language in the research study that informs you that it is original research:
These phrases show the reader that the authors of the article are the same ones who conducted the study and are presenting their original research. Original research articles are often referred to as Scholarly, Peer-Reviewed or Professional sources.
A review article is a secondary source.
A secondary source is one step removed from the original source (the research article). It reviews primary sources and does not present original research of its own. The review article reexamines, interprets and forms conclusions based on the information that is conveyed in the primary source. Review articles can suggest areas for new research, or identify patterns among existing research.
The purpose of a literature review article is to inform readers of the significant knowledge and ideas that have been established on a topic. Its purpose is to compare, contrast and/or connect findings that were identified when reviewing researchers' work.
The article linked above uses language that tells you it is not the original study but discussing research someone else has conducted.
The abstract of this article also indicates that it is a review article:
In Kaplan's book, Principles of Plant Morphology, he emphasizes that plant morphology is more fundamental than plant anatomy, which deals with tissues, cells, and subcellular components. His morphological principles are based on classical morphology. He devotes five chapters to leaf morphology, and points out that “organ differentiation is independent of the arrangement of cell and tissue types and even multicellularity itself” (Kaplan, 2022, p. 62).
Other language that indicates an article is a review and not an original study:
