Q.36 As per the Angiosperm Phylogeny Group (APG II, 2003) classification, which of the following plant
families comprises of only single genus with single species?
(A) Lauraceae
(B) Aristolochiaceae
(C) Amborellaceae
(D) Typhaceae
The correct answer is (C) Amborellaceae. According to the Angiosperm Phylogeny Group (APG II, 2003) classification, Amborellaceae stands out as the only family among the options with a single genus (Amborella) and a single species (Amborella trichopoda).
Option Analysis
Lauraceae (A): This family includes around 45-52 genera and approximately 2,850-3,500 species, such as Laurus nobilis (bay laurel) and Persea americana (avocado), primarily distributed in tropical and warm temperate regions. It fails the criterion of having only one genus and one species.
Aristolochiaceae (B): Recognized in APG II with multiple genera (at least 7-8, including Aristolochia, Asarum, and Thottea) and about 400 species, this family features distinctive pipe-shaped flowers and belongs to the order Piperales.
Amborellaceae (C): APG II explicitly defines this as a monotypic family containing solely the genus Amborella with its single species A. trichopoda, a shrub endemic to New Caledonia and positioned at the base of angiosperm phylogeny.
Typhaceae (D): In APG II (2003), this family consists of one genus (Typha, with about 12-15 species like cattails), while Sparganium remained in the separate family Sparganiaceae until merged in APG III (2009).
In the APG II 2003 classification system, identifying the plant family with only a single genus and single species is key for angiosperm phylogeny studies, especially for competitive exams like CSIR NET Life Sciences. This update to flowering plant taxonomy emphasizes monophyletic groups based on molecular data, placing basal lineages accurately.
Key Families in APG II
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Amborellaceae: Solely Amborella trichopoda, the most primitive extant angiosperm, lacking vessels in xylem and highlighting evolutionary insights.
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Lauraceae: Diverse with 45+ genera (e.g., Cinnamomum), over 2,800 species; economically vital for spices and timber.
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Aristolochiaceae: 7+ genera, ~400 species; known for trap-like flowers attracting pollinators.
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Typhaceae: Monogeneric (Typha) but multispecific (~12 species); aquatic herbs in Poales.
Exam Relevance
APG II questions test understanding of monotypic families, crucial for molecular systematics and basal angiosperm evolution in CSIR NET syllabi. Amborellaceae’s unique status underscores its role as a “living fossil” in phylogeny.
