The syllabus for the UPSC Botany Optional subject is as follows:

Paper-I:
1. Microbiology and Plant Pathology
- Structure and reproduction of bacteria, fungi, and viruses
- Classification and identification of plant pathogens
- Pathogenesis and disease resistance in plants
- Role of bacteria, fungi, and viruses in agriculture and industry

2. Cryptogams
- Classification, morphology, and reproduction of algae
- Classification, morphology, and reproduction of fungi
- Classification, morphology, and reproduction of bryophytes and pteridophytes
- Economic importance of algae, fungi, bryophytes, and pteridophytes

3. Phanerogams: Gymnosperms
- Classification, morphology, and reproduction of gymnosperms
- Distribution, affinities, and economic importance of gymnosperms

4. Plant Anatomy and Embryology
- Tissue organization and cell types in plants
- Anatomy of roots, stems, leaves, flowers, and fruits
- Development of embryo and endosperm in angiosperms
- Pollination, fertilization, and seed development

5. Plant Physiology
- Water relations in plants
- Mineral nutrition and transport in plants
- Photosynthesis and respiration
- Growth and development in plants
- Plant hormones and their role in growth and development

Paper-II:
6. Ecology and Plant Geography
- Ecosystem, community, and population ecology
- Ecological adaptations in plants
- Biotic and abiotic factors influencing plant growth and distribution
- Conservation and management of natural resources

7. Genetics, Plant Breeding, and Biotechnology
- Mendelian genetics and genetic mapping
- Chromosomal aberrations and mutations
- Plant breeding methods and objectives
- Genetic engineering and biotechnology in plant improvement

8. Economic Botany
- Medicinal and aromatic plants
- Fiber and oil-yielding plants
- Economic importance of cereals, pulses, and vegetables
- Plant resources for energy production

9. Biotechnology and Plant Pathology
- Microbial genetics and genetic engineering
- Molecular methods in plant pathology
- Plant diseases and their management strategies
- Biotechnological approaches in plant disease control

10. Physiology and Biochemistry
- Enzymes and plant metabolism
- Photosynthesis and photorespiration
- Nitrogen metabolism and nitrogen fixation
- Secondary metabolites and their functions in plants

The syllabus covers various aspects of botany including microbiology, plant pathology, cryptogams, phanerogams, plant anatomy, plant physiology, ecology, plant genetics, plant breeding, biotechnology, economic botany, and plant biochemistry. It is important to thoroughly understand and study each of these topics to excel in the UPSC Botany Optional subject examination.