异喙菊(Heteracia szovitsii)是分布于新疆北部荒漠、具短寿命花和多态果实的菊科一年生短命植物。本文对该物种的开花式样和花部特征以及繁育系统与昆虫传粉特性进行了研究, 以期明确其头状花序中小花的形态差异及其与多态果实间的关系、揭示其在短的花寿命内的繁殖特性。结果表明: 该物种头状花序中发育成多态果实的3类小花在数量、冠毛的有无以及舌片长/宽、子房宽、花柱裂片长和子房喙长之间均存在不同程度的差异, 且3类小花冠毛的有无以及子房宽和喙长与多态果实的形态一致, 说明多态果实的数量与形态在小花发育过程中就已完成分化。花序中的小花每天集中在上午开放, 使花序在功能上犹如一朵花, 可快速增大花展示和对传粉者的吸引, 以使异交在开花后短时间内完成; 3类小花的自花花粉均可在花柱裂片上萌发并长出花粉管, 说明该物种自交亲和。3类小花不去雄套袋后均能结实, 且自然授粉后的结实率显著高于不去雄套袋的, 说明该物种能自主自花授粉, 且异花授粉促进了结实。3类小花通过雄性先熟以及次级花粉呈现中的泵/刷机制, 将花粉呈现在花柱上部和未展开的柱头裂片外侧刷状毛上以及裂片顶端, 延长了花粉呈现(雄性阶段)持续的时间, 减少了花内雌雄功能间的干扰, 有利于传粉者异花传粉, 提高了雄/雌性适合度; 同时, 柱头裂片展开时可将自花花粉落置到裂片上, 以完成自主自花授粉。主要传粉者六显甜花蜂(Halictus sexnotatulus)的访花时间与花序开放时间、花粉活力最高期和柱头最佳授粉期高度吻合, 有利于雄性阶段花粉的输出以及雌性阶段柱头接受花粉, 保障授粉在开花后短时间内快速有效地完成以及异交成功。在新疆北部荒漠的春季环境中, 具短寿命花的异喙菊既可在低温多风导致传粉者不足或活动受限时, 通过快速自主自花授粉及自交亲和机制来提供繁殖保障, 也可在传粉者活动正常时, 通过集中开花、雄性先熟及次级花粉呈现等机制来快速完成异交, 提高雌/雄性及后代的适合度。

Heteracia szovitsii (Asteraceae) is a common ephemeral annual species occurring only in desert regions of northern Xinjiang in China, with short-lived florets and achenes within a single infructescence (capitulum) having three different morphs. To explore the relationship between morphological differences in florets and the polymorphic fruits and reproductive characteristics, we compared floral traits, flowering pattern, and flower visitors to the three floral morphs in H. szovitsii, and reproductive efforts by hand pollination treatments. The results showed that: Peripheral and intermediate florets did not have pappus, while central florets did. Number of florets and length and width of ligules were significantly different among the three floral morphs in a single capitulum. Further, the length of stigma lobes of peripheral florets was significantly greater than that of central florets, the length of ovary beaks of central florets was significantly greater than that of peripheral and intermediate florets. Differences in morphology with or without pappus, width of ovaries, length of ovary beaks among three morphs of florets were consistent with those of three morphs of achenes. These results indicated that the numbers of three morphs of achenes and their morphology had differentiated during the development period of three kinds of florets. The concentrated flowering pattern of blooming in the morning of three kinds of florets within capitulum, made the capitulum act as functional units, i.e. like a flower, thereby increasing flower display and attracting pollinators. Pollinator visits may facilitate outcrossing during the short flower longevity. Pollen grains of the three floral morphs could germinate and produce pollen tubes on their stigma lobes, indicating that this species is self-compatible. The three kinds of florets bagged without emasculation all can produce achenes, but fruit-set was all significantly lower than that of natural pollination, suggesting that this species could be autogamous and cross-pollination could increase fruit set. Due to the protandrous and the pump/bush mechanism of secondary pollen presentation, pollen of three floral morphs was present at the apex of the stigma and on the brush of hairs of both the upper part of style and outside lateral of the closed stigma lobes. This character prolonged the duration of pollen presentation (male stage), and reduced the interference between male and female functions within flower, promoted cross pollination, thereby improving male/female fitness. Meanwhile, it could allow the pollen deposition on the lobes when the stigma lobes expanded to complete self-pollination autonomously. Halictus sexnotatulus was the most frequent floral visitor, and the duration time among insects visiting, inflorescence opening, highest pollen viability and the highest stigma receptivity had a high degree of synchronicity. This strategy facilitated the output of pollen at the male stage and receipt of pollen on the stigma at the female stage, thus ensuring that pollination was completed quickly and effectively in a short time after flowering and that outcrossing was successful. In the desert spring environment of the northern Xinjiang, H. szovitsii with short-lived florets can not only provide reproductive assurance via autonomous self-pollination quickly under the condition of the lack of pollinators and/or limited activity due to low temperatures and windy conditions, but also can provide the opportunities for outcrossing, through concentrated flowering, protandry and secondary pollen presentation when environmental conditions became favorable for pollinator activities.