Part of CL-04 — Morphology & Anatomy of Flowering Plants

Exception and Special Cases

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Exceptions to General Rules:

RuleExceptionNotes
Monocots have parallel venationSmilax, Alocasia, Colocasia have reticulate venationMonocots in Araceae/Liliaceae-related families
Dicots have reticulate venationCalophyllum (Clusiaceae) has parallel venationFew dicot exceptions exist
Fabaceae has diadelphous stamensCassia (Caesalpinioideae) has free (polyandrous) stamensCassia tested in NEET 2016
Fabaceae has vexillary aestivationCassia has imbricate aestivationCassia NOT papilionaceous
Monocots cannot undergo secondary growthDracaena, Yucca undergo anomalous secondary growthVia primary thickening meristem — not true vascular cambium
Xylem parenchyma is the only living xylem elementIn some plants, parenchyma may be found transfusion tissue in gymnosperm leavesSpecifically in gymnosperm needle anatomy
Companion cells are paired with sieve tubesGymnosperms have albuminous cells (not companion cells) insteadAlbuminous cells are functionally analogous
Asteraceae has inferior ovaryMost Asteraceae have inferior, but some have semi-inferiorGenerally considered inferior in NEET
Stomata absent in submerged aquatic plantsVallisneria (submerged) has stomata in some partsComplex exception
Root hairs are from root epidermal cellsIn orchids, aerial roots have velamen (multilayered absorptive epidermis)Velamen absorbs moisture from air

Special Note on Cassia (Critical for NEET):

  • Cassia is listed as a Fabaceae example in NCERT
  • But its aestivation is IMBRICATE (not vexillary)
  • Its stamens may be free or only partly fused (not perfectly diadelphous)
  • Cassia belongs to sub-family Caesalpinioideae within Leguminosae
  • NEET 2016 tested this distinction — knowing Cassia has imbricate aestivation is important

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