Floral morphology and embryology of Helwingia (Helwingiaceae, Aquifoliales): systematic and evolutionary implications
Floral morphology and embryology of Helwingia (Helwingiaceae, Aquifoliales): systematic and evolutionary implications
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DOI：
10.1007/s10265-014-0672-9
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发表时间：
2015-01-01
影响因子：
2.8
通讯作者：
Tobe, Hiroshi
中科院分区：
文献类型：
--
作者：
Ao, Chengqi;Tobe, Hiroshi
Helwingia，一种分布于东亚的灌木或小乔木，有四种属，已被划分到不同的科，主要是山茱萸科。然而，分子分析表明，该属属于自己的 Helwingiaceae 科，是 Aquifoliales 目中的 Phyllonomaceae（仅限 Phyllonoma）的姐妹。以H. japonica为基础，我们研究了人们对Helwingia知之甚少的花和胚胎学特征，并将其与其他冬青科植物，特别是叶柄科植物的特征进行了比较。结果表明，Helwingia 的花被叶代表萼片，因为在拟形五瓣花中，它们的位置与 Phyllonoma 的五瓣花中的萼片（而不是花瓣）位置一致。基于现有信息的总体比较表明，虽然与叶柄花共有叶生花序、下子房和上雌圆盘蜜腺作为共形，但Helwingia的特征是花瓣缺失、倒瓣、大的下弯柱头、发育不良的圆盘蜜腺、细珠状胚珠，其成熟雌配子体充满浓密染色的细胞质，以及薄的成熟种子外套。形态学证据，就像分子证据一样，证实了 Helwingia 足够独特，可以归入自己的家族。形态学和实地观察表明，H. japonica 是通过风和昆虫授粉的，这是冬青目中第一个两亲性的例子。
Helwingia, a shrub or small tree of four species distributed in East Asia, has been assigned to various families, mainly Cornaceae. However, molecular analyses show that the genus belongs to its own family Helwingiaceae which is sister to Phyllonomaceae (Phyllonoma only) in the order Aquifoliales. On the basis of H. japonica, we investigated the poorly understood floral and embryological characters of Helwingia, and compared their features with those of other Aquifoliales, particularly those of Phyllonomaceae. Results showed that perianth leaves of Helwingia represent sepals, because in plesiomorphic pentamerous flowers, they agreed in position with sepals (not with petals) in pentamerous flowers of Phyllonoma. Overall comparisons based on available information show that, while sharing with Phyllonoma the epiphyllous inflorescence, the inferior ovary, and an epigynous disc nectary as syapomorphies, Helwingia is characterized by loss of petals, obhaplostemony, large recurved stigmas, poorly developed disc nectary, tenuinucellate ovules with a mature female gametophyte filled with densely stained cytoplasm, and a thin mature seed coat. Morphological evidence, like molecular evidence, confirms that Helwingia is sufficiently distinct to be placed in its own family. Morphological and field observations suggest wind and insect pollination in H. japonica, which is the first example of ambophily in Aquifoliales.