A key, whether dichotomous (a series of questions that can be answered true or false) or simple (a set of descriptive statements from which a best answer is chosen), can help you decide which parts of the plant are important to photograph.
First use an app or a “best guess” to get to the genus level. Then consult a plant key, either online or in print, suitable for your region. Do your best to key it out to the species level. Don’t focus on getting an accurate ID. Instead look for the traits that characterize major groups of species within each genus. Try to understand which features distinguish one species from other similar species. These may include:
Leaves
• Leaf form and arrangement https://www.deanza.edu/faculty/heyerbruce/b6c_pdf/LeafForms.pdf
• leaf size (include something to indicate scale, such as a pen or a ruler
• leaf venation, front and back
• leaf margins: smooth, serrated (what type of serration)
• presence of hairs on leaf surface, petioles, or on stem
Plant form
• size (height and width) of mature plant; include something to indicate scale (for large plants/trees this would be a landscape shot
• form/shape of mature plant (mounding, upright, columnar, broad, sprawling… )
• for trees and shrubs: bark colour and texture/patterning (helpful in winter)
Stems and twigs
• stems: is the cross section round, square, grooved, or ‘winged’
• growth from axils?
• twigs: slice the twig lengthwise and photograph the pith (center of the twig)
• Leaf scars (trees and shrubs) https://arboretum.ca.uky.edu/blog/fingerprints-leaves
Reproductive parts
• fruits
• flowers: the flower arrangement on stem, closeup of flower, underside of a flower, colour
• seeds: spent flowerheads, seeds, etc. Note the season of bloom or seed maturity
• conifers: cones
Note the nodding capitulescence (flower cluster) at the top of each stem.
For example, let’s say you know your plant is a Solidago (goldenrod) and your key lists 25 species. The first couplet (pair of either/or statements) describes the arrangement and location of the flowers. One group of (14) species has nodding groups of flower heads at the very top of stems and/or branches with flowers that all point to one side. The other group does not have these traits. (details here: https://gobotany.nativeplanttrust.org/dkey/solidago/#c1,c2). So it would be important to take a photo showing the location of the flowers clusters and whether the flowers all point to one side.
Delving further into the Solidago key, we learn that an important feature is the size and arrangement of leaves along the stem. Some species have large basal leaves that become progressively smaller going up the stem; some have similarly sized leaves all along the stem and no basal cluster. So it would be important to show the base of the plant as well as the size of leaves along the length of the stems.
Exploring the traits listed for similar species in a dichotomous key will not only introduce you to botanical terms but will also increase the likelihood of obtaining an accurate ID based on your photos, whether you submit them as observations in Inaturalist, a request an ID on social media, or show them to an expert botanist.
Resources
Plant Identification Basics: https://www.montana.edu/extension/invasiveplants/documents/publications/extension_publications/Plant%20identification%20basics.pdf
Anatomy and Morphology: https://content.ces.ncsu.edu/extension-gardener-handbook/3-botany#section_heading_6936
How to photograph plants: https://www.segrasslands.org/recording-species-in-inat-website
New York Botanical Garden guide to photographing plants: https://libguides.nybg.org/plantidphoto