Disjunct clades between the southern and the tropical Andes represent a biogeographical pattern that has not been studied. One of the plant groups showing this disjunction is the clade formed by the genera Archidasyphyllum, Arnaldoa and Fulcaldea (Asteraceae, Barnadesioideae). Archidasyphyllum is distributed in central and southern Chile and adjacent Argentina and is sister to the latter two, which in turn form a clade centered in northern Peru and southern Ecuador, with one species of Fulcaldea in Bahia, Brazil. The western American clades are separated by a distance of ca. 2500 km in direct line and have no representatives through the entire arid and hyperarid regions of the Pacific deserts and the dry Puna. We hypothesized that the Neogene origin of aridity in this intervening area might be responsible for this disjunction. To address this hypothesis, we estimated divergence times and ancestral range and quantified the climatic niches of the respective clades and compared them to each other and with the intervening area. Our results suggest a Miocene split of this clade from an ancestor previously distributed in the Central Andes, where the species of this clade are currently absent. Colonization of NE Brazil by Fulcaldea may have occurred during the Pliocene. The niche analysis rejects climatic niche conservatism and the intervening area is found to be climatically different from the current ranges occupied by either clade. We suggest that the global cooling trend in the Miocene and concomitant hyperaridity in the Pacific deserts and southern Central Andean highlands played a crucial role in the formation of this disjunct pattern and that the climatic niches of each clade have subsequently shifted in different directions.

南部安第斯山脉和热带安第斯山脉之间的分离分支代表了尚未研究的生物地理格局。表现出这种分离的植物群之一是由弓形藻，Arnaldoa和Fulcaldea属（菊科，Barnadesioideae）形成的进化枝。Archidasyphyllum分布于智利中部和南部，与阿根廷相邻，是后两个的姊妹，后者则形成了一个以秘鲁北部和厄瓜多尔南部为中心的进化枝，其中有一种富尔卡地亚（Fulcaldea）在巴西巴伊亚州。美洲西部的进化枝之间相距约ca. 直线距离为2500公里，在整个太平洋沙漠和干旱的普纳（Puna）的整个干旱和高干旱地区没有代表。我们假设在这个中间区域的干旱的新近纪起源可能是这种分离的原因。为了解决这个假设，我们估计了发散时间和祖先范围，并对各个进化枝的气候生态位进行了量化，并将它们彼此之间以及与居间区域进行了比较。我们的研究结果表明，该进化枝的中新世从先前分布于安第斯山脉中部的祖先中分离而来，目前该进化枝的物种不存在。Fulcaldea对巴西东北部的殖民可能是在上新世期间发生的。生态位分析拒绝了气候生态位保守性，并且发现中间区域在气候上不同于任一进化枝所占据的当前范围。我们认为，中新世的全球冷却趋势以及太平洋沙漠和安第斯中部南部高地伴随的高干旱在这种分离模式的形成中起着至关重要的作用，每个进化枝的生态位随后向不同的方向转移。