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The following points highlight the thirty-six important Swingle’s principles for plant classification.
Swingle’s Principle # 1. Plant relationships are up and down genetic lines and these must constitute the framework of phylogenetic taxonomy.
Swingle’s Principle # 2. Some evolutionary processes are progressive while others are regressive.
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Swingle’s Principle # 3. Evolution does not necessarily involve all organs of the plant at one time or in the same direction.
Swingle’s Principle # 4. Evolution has generally been consistent and when a particular progression or regression has set in, it is persisted into the end of the phylum.
Swingle’s Principle # 5. In any phylum the chlorophyll bearing plants precede the chlorophyll less ones.
Swingle’s Principle # 6. Usually structures with many similar parts are more primitive, and those with fewer and dissimilar parts are more advanced.
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Swingle’s Principle # 7. In seed plants the stem structure with collateral bundles arranged in a cylinder is more primitive than the scattered bundles.
Swingle’s Principle # 8. Scalariform vessels are more primitive than vessels with round pits.
Swingle’s Principle # 9. In most groups of seed plants woody members have preceded the herbaceous ones.
Swingle’s Principle # 10. In most groups of seed plants erect members have preceded the vines.
Swingle’s Principle # 11. Perennials are more primitive than biennials and biennials are usually more primitive than annuals.
Swingle’s Principle # 12. The spiral arrangement of leaves precedes that of opposite and whorled types.
Swingle’s Principle # 13. Simple leaves are more primitive than compound leaves.
Swingle’s Principle # 14. Deciduous leaves are advanced.
Swingle’s Principle # 15. Netted venation of leaves is more primitive than the parallel venation.
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Swingle’s Principle # 16. The many-parted flower is more primitive, the type with few parts being derived from it, and the change is accompanied by a progressive sterilization of sporophylls.
Swingle’s Principle # 17. Perianth of similar segments is more primitive than one in which sepals and petals are unlike each other.
Swingle’s Principle # 18. Flowers with petals preceded apetalous ones, the latter being derived by reduction.
Swingle’s Principle # 19. Polypetalous flowers are more primitive than gamopetalous ones, the latter being derived from the former by symphysis.
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Swingle’s Principle # 20. Actinomorphic flowers are more primitive than zygomorphic ones.
Swingle’s Principle # 21. Spirally imbricate floral parts are more primitive than that of whorled and valvate.
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Swingle’s Principle # 22. Hypogyny is the primitive and from it perigyny and epigyny have been derived.
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Swingle’s Principle # 23. Numerous carpels are more primitive condition than a few carples.
Swingle’s Principle # 24. Separate carpels are primitive condition than united carpels.
Swingle’s Principle # 25. Axile placentation preceded parietal and central placentation.
Swingle’s Principle # 26. Numerous stamens indicates a more primitive condition than that of a few stamens.
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Swingle’s Principle # 27. Separate stamens preceded united stamens.
Swingle’s Principle # 28. Evolution is believed to have proceeded from seeds with two seed cotyledons to those with only one.
Swingle’s Principle # 29. The primitive seed contains endosperm and a small embryo, the advanced type has little or no endosperm, with the food stored in a large embryo.
Swingle’s Principle # 30. A straight embryo is primitive than a curved one.
Swingle’s Principle # 31. The solitary flower is more primitive than the inflorescence.
Swingle’s Principle # 32. Bisexual flowers preceded unisexual flowers.
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Swingle’s Principle # 33. The monoecious is primitive than dioecious.
Swingle’s Principle # 34. Simple and aggregate fruits preceded multiple fruits.
Swingle’s Principle # 35. The same evolutionary phenomena have often been repeated as separate occurrences in different parts of the plant kingdom e.g. loss of petals, stamens and carpels; a change from simple to compound leaves, hypogynous to perigynous or epigynous insertion of floral parts.
Swingle’s Principle # 36. In determining the close relationship between two families or other groups, it is usually best to compare with each other the most primitive, or basal members of each group.
