Degradation of the upper pulvinus in modern and fossil leaves of Cercis (Fabaceae).
Degradation of the upper pulvinus in modern and fossil leaves of Cercis (Fabaceae).
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DOI：
10.2307/2446316
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发表时间：
1998-02
影响因子：
3
通讯作者：
S. Owens;P. Fields;F. Ewers
中科院分区：
文献类型：
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作者：
S. Owens;P. Fields;F. Ewers
根据叶片基部（上叶枕）是否存在叶枕，将化石叶印鉴定为紫荆属一直受到质疑。在本研究中，加拿大紫荆的叶片进行了检查之前和之后的脱落，以探讨退化过程中可能发生的脱落之前，并相应地修订了北美记录的紫荆化石叶。C.结果canadensis指出：（1）枕大部分由非木质细胞组成（一个宽的皮层，一个非木质纤维鞘，韧皮部，和髓），在叶脱落后迅速降解，（2）木质木质部组织，在降解后留在叶枕中是脆股，（3）叶枕降解速度比叶片或叶柄快，（4）退化的枕垫在椎板上留下半圆形图案。通过对化石和现存物种的研究，我们：（1）证明在化石中，上部枕可以比相邻的叶柄或叶片组织表现出更大程度的降解，这表明上部枕组织的降解在现代标本与化石标本中是相似的，（2）定义了许多其他可以结合使用的层状特征，或在没有的情况下，（3）根据这些标准，本研究新报道的一个标本表明，北美最早的紫荆属植物叶化石记录来自俄勒冈州的Succor Creek植物群。
Identification of fossil leaf impressions as Cercis has been questioned based upon the presence or absence of a pulvinus at the base of the lamina (upper pulvinus). In the present study, leaves of Cercis canadensis were examined before and after abscission to explore the degradation processes that could occur prior to fossilization, and the North American record for fossil foliage of Cercis was revised accordingly. Results for C. canadensis indicate that: (1) the pulvinus consists largely of tissues with nonlignified cells (a wide cortex, a nonlignified fiber sheath, phloem, and pith) that degrade rapidly after leaf abscission, (2) the lignified xylem tissue that remains in the pulvinus after degradation is in brittle strands, (3) the pulvinus degrades at a faster rate than the lamina or the petiole, and (4) the degraded pulvinus cushion leaves a semicircular pattern on the lamina. From examination of fossils as well as extant species, we: (1) demonstrated that in fossils, the upper pulvinus can show a greater degree of degradation than the adjoining petiole or lamina tissue, suggesting the degradation of upper pulvinus tissue is similar in modern vs. fossil specimens, (2) defined numerous other laminar characters that can be used in conjunction with, or in the absence of, an upper pulvinus to confirm the presence of Cercis in the fossil record, and (3) showed from those criteria that the earliest known North American fossil leaf record for Cercis, from a specimen newly reported in the present study, is from the middle Miocene Succor Creek flora of Oregon.