Aponogeton microphyllus, previously placed under the synonymy of A. undulatus, is recognized here as a distinct species based on morphology, chromosome number, and molecular phylogenetics (nuclear ribosomal internal transcribed (ITS) spacer region). Observations on the type and live specimens revealed morphological differences between the two species. Aponogeton microphyllus flowered regularly and set seeds. Aponogeton undulatus flowered rarely, did not set seeds, but showed formation of young plantlets on the inflorescence axis. Similarly, different chromosome numbers were recorded in Aponogeton microphyllus and the two forms of A. undulatus, viz., AF1 and AF2, which occur in distinct populations. Aponogeton microphyllus exhibited polysomaty with root-tip cells showing 2n=40, 42, and 44 chromosomes. The two forms of A. undulatus, AF1 and AF2, showed 2n=84 and 86 chromosomes, respectively. Based on the ITS data, both species occupied two separate clades. Plastid trnK intron region indicated a close relationship between both species. Our study suggests the need for comprehensive phylogenetic analyses of A. undulatus across its distribution range based on more advanced techniques such as high-throughput sequencing data to understand the A. undulatus species complex and to detect natural hybrids of this species.

Aponogeton microphyllus以前被归为A. undulatus的同义词，现在根据形态、染色体数目和分子系统发育学（核核糖体内转录 (ITS) 间隔区）被认为是一个独特的物种。对类型和活体标本的观察揭示了两个物种之间的形态差异。Aponogeton microphyllus定期开花并结籽。Aponogeton undulatus很少开花，不结种子，但在花序轴上形成幼苗。同样， Aponogeton microphyllus和A. undulatus的两种形式（即 AF1 和 AF2）中记录了不同的染色体数目，它们出现在不同的种群中。Aponogeton microphyllus表现出多体性，根尖细胞显示 2 n = 40、42 和 44 条染色体。波状 A. undulatus的两种形式，AF1 和 AF2，分别显示 2 n = 84 和 86 条染色体。根据 ITS 数据，两个物种都占据两个不同的分支。质体trnK内含子区域表明两个物种之间存在密切关系。我们的研究表明，需要基于更先进的技术（例如高通量测序数据）对波状 A. undulatus的分布范围进行全面的系统发育分析，以了解波状A. undulatus物种复合体并检测该物种的自然杂交种。