There are many directions you could take a natural form project to make it more interesting, meaningful and creative. Here are just a few ideas to get you thinking:
Portraiture
  •  Relationships between people and nature
Architecture
  •  Inspired by nature, e.g. Gaudi
  •  Buildings amongst nature
Life & Death
  •  Skeletons vs flowers
  •  Old versus new
Growth & Decay
  •  Old versus new
  •  Cycle of life
The Environment
  •  Global warming
  •  Pollution / plastics
  •  Deforestation
Still Life
  •  Bringing the outside inside
  •  Creative compositions
  •  Relationships between objects that have been placed together
The Weather
  •  Sun, rain, snow, storms/wind
  •  Natural disasters
  •  Ice formations
  •  Water droplets on plants and flowers
The Seasons / Passing of Time
  •  Passing of time
  •  Circle of life in nature
  •  Varying colours and light
  •  Linked to the weather
Animals in Nature
  •  Animal habitats
  •  Wild versus domestic
  •  Animal cruelty
  •  Endangered species
Abstract Compositions
  •  Inspired by natural forms
  •  Linked to texture
  •  Influenced by colours in nature
Surrealism / Dreams
  •  Imagination
  •  Storytelling
Insects
  •  Close-up
  •  The important role of insects
  •  Fantasy / Surrealism / Storytelling
  •  Spreading of diseases
Night versus Day
  •  Colour contrasts
  •  Different wildlife
Food
  •  Where food comes from (the food chain)
  •  Ethics (e.g. vegan or supporting local farms)
Furniture Design
  •  Inspired by nature
Close-up / Macro
  •  Linked to texture
Music
  •  Inspired by nature and how it might be represented visually
Love / Romance
  •  Link between flowers and romance
Travel
  •  Cultural identity
  •  Exploration / acquisition of knowledge
Diversity
  •  Different cultures
  •  Colours linked to homophobia, pride, racism or other forms of prejudice
Trees
  •  Age
  •  Passing of time
  •  Strength and stability
  •  Home for wildlife
Gardens
  •  Botany
  •  Allotments
  •  Humans nurturing nature
  •  Wildlife
Occasions
  •  Roses = Valentines
  •  Lilies = Peace
  •  Poppies = Remembrance
Symbolism
  •  What different flowers represent
Intertwined
  •  Connections
  •  Relationships
  •  Intimacy and romance
Growth Mindset
  •  Positivity
  •  Outlooks on life
Geography
  •  Climates
  •  Water cycle
  •  Clouds
  •  Geology
  •  Natural Disasters
Poisonous Plants
  •  Danger
  •  Evil
  •  Deceit
  •  Crime / revenge
Religion & Ethics
  •  Good versus evil
  •  Hope
  •  Sin
  •  Kindness
Storytelling
  •  Imagination
  •  Illustration
This list is not exhaustive, so use it for inspiration but don't let it limit your ideas.